On average Chicagoans can expect three intense cold waves every winter, and most do not last long (though, admittedly, they last long enough for the fancy of most of us). In the Chicago area they are unlikely to last more than four days. However, the cold wave that descended on Chicagoland on the last day of 2009 and continues today is giving strong indications that it's going to linger well beyond the normal four-day life span. Strong winds from the north and northwest at the 20-30 thousand foot level -- the level of "steering winds," so-called because they direct the movement of air masses at the surface -- are likely to persist for 7-12 days. In response, air masses originating from the frigid reaches of northern Canada will dominate Chicago's weather through that period.
Lake-effect snow to bury northern Indiana
Northwesterly winds and persistent cold at Chicago invariably mean persistent lake-effect snow in the snowbelt areas of northern Indiana and southwest Lower Michigan. Impressive snow totals, possibly measured in feet, are likely there in coming days.
Dear Tom,
My mother says she remembers a terrible ice storm in Chicago that occurred on New Year's Eve. What year was that?
Kendra Rasmussen
Dear Kendra,
Chicago's worst-ever ice storm began just after 1 a.m. on Jan. 1, 1948. With temperatures hovering around freezing, a steady rain quickly coated the city with nearly a half inch of glaze. The rain became mixed with sleet, adding to the icing woes. Strong winds gusting to 60 coupled with the weight of the ice brought down trees and power lines. Several large radio transmission towers also crashed down.
Roads were so slippery that all traffic, except for emergency vehicles, was ordered off the streets. Adding to the day's misery, nearly five inches of snow fell on top of the ice later that day. In one ironic twist, a New Year's Day city ice skating championship had to be canceled due to the ice storm.
The season's chilliest and most enduring cold-air outbreak begins this morning with the arrival of arctic air that sends temperatures steadily downward through the day. A reading of 13 degrees is likely at the stroke of midnight as we usher in 2010 - cold but a far cry from the minus 10 that prevailed at midnight on Dec, 31, 1967.
The chill will last for several days, setting the stage for massive lake-effect snow accumulations in the Indiana snow belt. A multi-day total of three feet of snow is possible by early next week.
Blue Moon shines tonight
Get ready to celebrate the arrival of 2010 with a blue moon. According to popular definition, a blue moon is the second full moon in a month. It won't be blue, of course -- the name has nothing to do with the color of our closest celestial neighbor. A full moon occurred on Dec. 2 and another occurs today, and this December's blue moon is the first since May of 2007. New Year's Eve blue moons are much more rare, occurring only every 19 years. The last one was in 1990 and the next won't come until 2028. Triton College astronomer Dan Joyce points out that blue moons have no astronomical significance,
Dear Tom,
After a trip to Oahu (the island on which Honolulu is located), my parents said rainfall varies greatly from one side of the island to the other. There is even a song about the windward and leeward sides, but they have not been able to find the song. It's a long shot, but can you identify that song?
Bill Frank
Dear Bill,
The song is "Island Style" by John Cruz, who, incidentally, grew up on Oahu. The lyrics that caught your parents' attention are:
"On the Island, we do it Island Style, from the mountain to the ocean, from the windward to the leeward side."
However, the song does not refer to Oahu's climate; rather, it's a celebration of the laid-back Hawaiian life style. Because northeast trade winds dominate Oahu's climate, the northeast-facing (windward) coast and mountains are awash with 60-280 inches of rain annually, whereas the southwest (lee) coast receives only 8-15 inches.
Tuesday's brief respite from the clouds and snow, dominate meteorological features of December 2009, is coming to an end. Area residents reveled in Chicago's sunniest weather of the past 13 days Tuesday. The day hosted 88 percent of its possible sunshine and managed a 24-degree high. But the thickening, wintry-gray cloud deck under development as Wednesday gets underway is to begin producing snow by late morning or early afternoon--snow which is likely to continue in periods through Wednesday night. Computer snowfall estimates for the Chicago come in at half an inch to an inch and a half. But another technique employed by forecasters to estimate possible snowfall is less conservative, generating amounts by daybreak Thursday (New Year's Day) closer to 4 to 5 inches.
This method---the B.J. Cook Technique---looks at the degree to which temperatures warm high in atmosphere at 39,000 ft. and relates that warming to snowfall. Studies have found that peak snowfall at ground level often ends up equaling half the temperature increase more than 7 miles above the ground. That rising temperatures aloft can be related to snowfall intensity makes sense when you think about. Disturbances in the atmosphere produce precipitation by encouraging moist air to rise and saturate, producing rain or snow and clouds. Rising air transports warmer temperatures aloft. Therefore, the AMOUNT of warming aloft offer a means of gauging just how vigorously air is rising which, in turn affect the intensity with which precipitation falls. The stronger the updrafts, the greater the amount of moisture which rushes into an area and, therefore, the higher the amount of that moisture which precipitates out as rain or snow.
A "wall" of frigid arctic air hits toward News years Eve (Thursday evening)
A blast of frigid arctic air is the next weather challenge facing Chicagoans this week. While high temperatures are likely to hover around 30-degrees Thursday afternoon, the leading edge of bitterly cold air is to ride gusty northwest winds into the area toward New Year's Eve. From that point forward, temperatures are expected to dive. Single digits are likely Friday (New Year's Day) with the day's temperature recovery only resulting in highs in the teens. Nighttime lows in single digits or sub-zero are predicted Friday and Saturday nights. Days of northwest winds across Lake Michigan are likely to ignite waves of lake snow which may---between Friday and night and next Tuesday---produce heavy accumulations in excess of a foot in a number of locations.
The chill is Florida-bound
The frigid outbreak is to plunge into the Southeast and out over the Gulf of Mexico and into the Caribbean. Freezing nighttime readings are likely to reach sections of north and central Florida this weekend. The cold's intensity is likely to wane once in contact with the warm ocean waters to the south of Florida--but it is likely to shift winds as far south as Cuba, Mexico's Yucatan Peninsula and even Jamaica to the northeast over the weekend and into next week.
Dear Tom,
Didn't we tie or break a record for consecutive snowy days last January?
Tim Benshoof
Dear Tim,
You are absolutely correct. Chicago recorded measurable snow for nine straight days earlier this year from Jan. 6-14. The nine day snowfall total was 18 inches with most of that falling in a two-day storm on January 9-10 that buried the city with a foot of snow. That string of nine snowy days equaled a stretch logged back in 1902, when measurable snow was observed from Jan. 29 to Feb. 6. However the total snowfall then was only 5 inches with most days getting just a dusting. You may remember that bitterly cold weather followed the snowy period last January with the mercury dropping to minus 18 at O'Hare International Airport on Jan. 16. Many suburban areas were much colder with Joliet falling to 30 below zero and Barrington to minus 23.
Tuesday's unlimited sunshine is likely to put a bounce in the step of many Chicagoans while dazzling still others. No wonder! Sunshine's been an incredibly rare commodity here, especially over the past 12 days. December 2009 has been the cloudiest and least sunny of any December in two years. For sunshine to be in short supply this month isn't a surprise. December has historically been the area's cloudiest month---but this year's limited sun is paltry even by December's undemanding standards. Through sunset Monday, only 3,994 of the month's possible 15,475 minutes of sun occurred here, reports veteran National Weather Service observer Frank Wachowski. That's just 26 percent of the area's possible sunshine--far from the 39 percent most Decembers produce. Over 7 consecutive days--from Dec. 17 through Dec. 24---the sun never even put in an appearance. Fleeting rays did show up for 10 minutes Dec. 25 only to disappear Dec. 26, then appear for a fleeting 8 minutes on Dec. 27.
Lack of sun not the only story--December snow has been plentiful
This month's nearly 20 inches of snow is almost three times the normal tally of 7.4 inches through Dec. 20--heavy enough to rank the 9th snowiest Dec. 1-28 period in 125 years. Not only is the tally to date impressive but the frequency of measurable snows this month has been running at twice the average pace. There have 12 days with at least 0.1-inches (the amount considered "measurable" snow) compared to the long term average of 6.
But the break in the weather Tuesday may not last long. A new weather system is targeting the Midwest with snow Wednesday afternoon into Thursday followed by an outbreak of frigid arctic air likely to render New Year's Eve and Day (Thursday evening and Friday) more than a bit nippy.
Early thinking on potential mid-week snow accumulations
The system predicted to bring Chicago clouds and snow Wednesday afternoon into Thursday moved into the West off the Pacific Monday. It is predicted to cross the Rockies in coming days emerging in the Plains before making its move on the Midwest. Details of Chicago's potential mid-week snowmaker will become clearer as the system moves over land where weather balloons are able measure its structure with special clarity. Raw computer model snowfall estimates suggest an average of 2.2 inches of snow may fall here from the 0.14 inches of moisture the system is to produce. This suggests another dry, fluffy snow may be in the cards. But yet another snow accumulation forecast technique, which takes into account the rate at which temperatures change 39,000 ft. above the ground---the so-called B.J. Cook technique---hints at possible 3 to 5.5-inch tallies. Forecasters will be monitoring this system carefully in coming days.
December 2009 on the books as the city's 9th snowiest to date
December has already logged a monthly snowfall of 19.7 inches---nearly three times its long term (125-year) average average of 7.4 inches.
Dear Tom,
It seems like we haven't seen the sun in weeks. Is this December cloudier than normal? What is Chicago's cloudiest month?
Rich Bartecki Morton Grove
Dear Rich,
Even though December is the city's cloudiest month, December 2009 has indeed been much cloudier than normal in Chicago. Frank Wachowski, who tracks Chicago sunshine, reports that through Dec. 28 the city had received only 26 percent of the month's possible sunlight, far less than the normally dismal 39 percent. In fact, the city has logged a total of just 64 minutes of sun dating back to December 17. As cloudy as it's been here, there have been cloudier Decembers. December 1975 produced only 19 percent of the possible sunshine and the city's cloudiest month ever was Nov. 1988 with just 16 percent.
It will get colder as 2009 draws to a close, but Chicagoans beleaguered by a six-day stretch of winter weather woes can finally look forward to some quieter days ahead. Some snow flurries may linger Monday, but a rare sunny day is on tap for Tuesday, breaking a nearly two-week stretch of sunless skies. A touch of snow could return here Wednesday night ahead of a new surge of arctic air, but it should be gone Thursday morning with dry but cold conditions expected for New Year's Eve celebrations. A frigid start is anticipated for 2010 with subzero lows possible -- especially over heavily snow-covered areas -- by next weekend.
Snow expected south of the border
Another low-latitude storm, so typical of an El Nino winter, will sweep across the Southwest Tuesday, bringing a threat of significant snow from southern New Mexico to the Big Bend area of Texas. Winter storm watches are posted for 1-2 inches of snow in the lower elevations and up to 8 inches in the mountains. Snow or a rain/snow mix could even fall in adjacent portions of Mexico.
Dear Tom,
I see that the second full moon this month will be on New Year's Eve. Has this ever happened before?
Lucy Thomson, Lake Forest
Dear Lucy,
A New Year's Eve full moon is a fairly rare event, but it has happened many times before. The last one was 19 years ago in 1990 and the one before that occurred back in 1971. After this year's Dec. 31 full moon we will have to wait until 2028, 2066, 2104, 2115, 2134 and 2180 for repeats. By nature of the moon's 29.5-day cycle, a New Year's Eve full moon will always be the second full moon of the month. Astronomer Dan Joyce of the Cernan Earth and Space Center at Triton College tells us that the odds are that a full moon will occur twice on a particular calendar date in any 59-year period.
Though greatly weakened, the Great Christmas Blizzard that blasted portions of the Plains and Upper Midwest with up to 2 feet of snow and 80 mph winds still had enough punch to drop up to a foot of snow on the northwest portions of the Chicago area. Hardest hit were areas northeast along a line from St. Charles to Arlington Heights where snowfall totals approached 12 inches. Amounts tapered off to the southeast with lesser but still substantial 2 to 6 inch amounts in the city and south suburbs.
High snow to water ratios behind Saturday's huge snowfall
The snow was incredibly dry and fluffy, allowing it to pile up rapidly. With snow to water ratios from Saturday's storm in the 30-40:1 range (one inch of water yields 30-40 inches of snow) the storm produced three to four times as much snow as a typical snowstorm in which an inch of water brings 10 inches of snow.
Another shot of snow possible Sunday
Another impulse rotating around the remnant Plains storm will reach the city Sunday and could generate another round of accumulating snow, this time in the 1 to 3 inch range.
Dear Tom,
What was the track of the low that brought Chicago its massive New Year's snowstorm in 1999?
Matt Balitewicz, East Chicago, Ind.
Dear Matt,
The crippling blizzard that officially brought Chicago 21.6 inches of snow followed a classic heavy snow track for Chicago. It formed in southeast Colorado New Year's Day, then traveled across far southern Missouri before turning northeast across Indiana and moving into Lower Michigan. During its trek across the Midwest, the storm ingested large amounts of Gulf moisture at the same time cold air was feeding into it on its northern flank, assuring the precipitation here remained snow. With strong northeast winds, lake effect added several inches to the final storm totals. This snowstorm remains the city's second greatest, surpassed only by the 23.0 inch "Big Snow" of Jan. 26-27, 1967.
Not even the warmest Christmas temperatures in 15 years which followed a night of wind-driven rain could deny Chicago a White Christmas Friday. The 1" of snow on the ground at O'Hare as the day dawned was enough to put Dec. 25, 2009, into the books as a White Christmas. But the warmth which fostered raindrops rather than snowflakes Friday morning succumbed to a rush of cold air into the area from the southwest beyond noon. Midday temperatures across Illinois Friday made it clear Chicago's mild air was in trouble. While O'Hare reported 42 degrees, readings in St. Louis to the south had plunged to 23, and Quincy, Ill., was shivering at 18.
Chicago's temperatures began a 10-hour, 20-degree plunge shortly before noon, registering 16 degrees of that drop in between noon and 6 p.m. The late morning high of 43 degrees had already put Christmas 2009 in the books as the mildest in 15 years -- and one of only two Christmases in the last decade and a half to reach the 40s.
After a morning of rain showers, snow was being reported at both the Midway and O'Hare observation sites just after 3 p.m. and an inch of snow had fallen by late evening in west suburban Batavia in the Fox Valley. Other 1" tallies were being reported to the west in and south in Ottawa, Freeport and Morrison.
Sunshine managed a brief appearance during the warm interlude Friday morning. The 10 minutes of sun at Midway Airport was the first here in 8 days. December 2009's record on sunshine has been dismal -- only 28% of the month's possible sun has occurred to date. That's safely above the record low of 19% but makes it the cloudiest December since the 24 percent recorded in 2007. The month typically sees 39% of its possible sun.
Snowy Saturday ahead including 2 to 4" accumulations
A mammoth winter storm centered in Iowa begins a slow eastward drift Saturday, circulating accumulating snow into the Chicago area into Saturday night. Computer models estimate precipitation is to total 0.30" during the period, and that the day's cold temperatures will support fluffier than usual snowflakes likely to produce accumulations between 2-4 inches. While snow is likely to be in the air frequently during the day, its intensity is likely to vary. Bursts of heavier snowfall under the storm's southern flank -- the region of the system Chicago will be in Saturday -- occasionally reduced visibilities to 1/2 to 1 mile. It's a set-up likely to be repeated here at times Saturday.
The so-called wrap-around snow is rotating out of a full-scale blizzard on the storm's back side which has crippled the Plains and far western Midwest. Accumulations there had reached 23" in Duluth late Friday and more than a foot over a wide swath of eastern Nebraska, Western Iowa, the Dakotas and west and northern Minnesota. Gusts hit 76 mph at Rapid City, and drifting snow closed many roads in the multistate region. Twenty deaths were being attributed to the storm late Friday.
Dear Tom,
What is the preferred indoor relative humidity during the winter?
Nolan Marg
Dear Nolan,
A good rule of thumb is to try to keep the indoor relative humidity in your home at about one half of the indoor temperature. If your house is heated to 70 degrees then the humidity in the house should be about 35 percent. When cold outside air is warmed to room temperature without additional moisture, the relative humidity level undergoes a significant decrease. It is not as critical when air temperatures are above 40 degrees, but once outdoor readings drop into the 30s or lower, a house can become "desert-dry" with the relative humidity dropping below 10 percent. When this happens, static electricity flourishes and many people experience dry skin and respiratory discomfort.
For only the second time in the past 15 years, Chicago is likely to
record a 40-plus-degree Christmas high -- a reading 17 degrees warmer than
a year ago and 9 degrees above normal. It's not a situation likely to
last. Big changes loom, including sharp cooling and the potential for
accumulating snow Friday night and over the weekend. Friday's
comparatively mild readings follow Thursday's limb-snapping, air
traffic-snarling ice storm which cut power to 21,000 area customers,
many of them in the northwest suburbs, while encasing vehicles which
remained out in the elements in a quarter to half an inch of ice. The
icy world through which Chicago area residents finished holiday
shopping Thursday followed a night of cold rain which fell from
40-degree clouds just 2,000 feet above local terrain. Temperatures by
Thursday evening had climbed above freezing as heavy rains made their
move on the area. Drenching overnight 1-2-inch downpours on top of
melting snow raised flood concerns. With the top layer of soil frozen,
the runoff has nowhere to go but to collect in low-lying areas or
overtaxed waterways.
Storm's blinding snow, near 70 mph gusts paralyze the Plains
The storm responsible for Chicago's damp, ugly weather is generating a
blizzard, described by forecasters in the region as a once-in-a-quarter-century-intensity storm, across the western Midwest and Plains. Travel in the
region will be all but impossible. A state of emergency was declared
Thursday across Oklahoma, crippled by full-blown blizzard conditions
which married 60-plus mph wind gusts and blinding snowfall, slashing
visibilities to zero.
Simultaneously, the storm spawned an outbreak of twisters in its warm
sector along the Gulf Coast from Texas to southern Mississippi. There
were 25 reports of tornadoes. A huge temperature spread -- from 81 degrees at
Hollywood, Fla., to -11 at Glasgow, Mont. -- was behind the atmospheric
mayhem. Temperatures plummeted on the storm's cold backside, falling
more than 40 degrees below previous-day levels in sections of Oklahoma
and Texas. In the Dallas/Fort Worth area, the first measurable
Christmas Eve snow ever -- 3 inches of it -- followed by just a day a high of 75 degrees. Stunning as that change was, it couldn't hold a candle to
the blizzard which raked Oklahoma just to the north. Oklahoma City was
buried beneath 14.1 inches of snow -- its heaviest snowstorm on record --
since weather observations were first archived in 1890. It was a shock
to residents accustomed to full-season snowfall there of just over 9 inches.
Indications Chicago is to see more than the usual "backside" snow with this storm
Storms which bury areas west of Chicago beneath big snows usually only
swipe this area with flurries. This storm may be different. A blocking
pattern over southern Canada is to bring the mammoth low pressure,
which lifted from Texas into Iowa Thursday, to a veritable halt in
coming days. It will loop in place over Iowa into Saturday -- one of the
more unusual developments of any storm in recent memory -- before
resuming an eastward drift toward Chicago. This will keep snows on its
west side falling heavily over a huge region of the Plains from eastern
Nebraska north to the Dakotas and western Minnesota for an extended
period, producing gargantuan accumulations-- some potentially in excess
of 20 inches. But it sets the stage for sticking snow in Chicago. The snow is
likely to fall periodically much of the weekend but is to fall most
heavily in two or three distinct waves. A series of techniques for
estimating possible snowfall suggests as much as 4 or more inches of
snow could fall in bursts over the coming 2-3 days here or nearby.
Dear Tom,
What is the difference between sleet, ice pellets and freezing rain?
Jesse Starkman
Dear Jesse,
Sleet is precipitation in the form of small grains of ice. It forms when raindrops (or largely melted snowflakes), originating in warmer air aloft, fall through a layer of subfreezing air at ground level and then freeze on their way down. Sleet is referred to as ice pellets in weather observations.
Freezing rain is rain, also originating in warmer air aloft, that falls into a shallow layer of subfreezing air (usually only several hundred feet deep) at the ground and freezes upon impact to form a coating of glaze on exposed objects.
Sleet and snow always present challenges for those who must cope with them, but when it comes to creating inconvenient, damaging and even life-threatening conditions, freezing rain is in a class by itself.
An ice-storm grips much of the Chicago area away from Lake Michigan as Thursday dawns. Tree limbs and power lines droop under the added weight of ice and are at risk of snapping as powerful winds with a mammoth winter storm whip through the region. Ice storms occur when warm, moist air moves into an area above a shallow layer of freezing or sub-freezing air. Temperatures have hovered in the upper 20s or low 30s at ground level over much of the area overnight while readings just 2,000 feet above the ground have surged into the mid 40s. It's a set-up which has allowed rain to form in the warmer clouds above which then falls into cold surface air below producing a glazing of ice on colder outdoor surfaces. Though road chemicals work well at these temperatures, ice can accumulate on untreated sidewalks, driveways, vehicles and other cold outdoor surfaces and extreme caution is advised when first encountering any surface exposed to the freezing rain.
Power outages were scattered across Rockford late Wednesday evening and flooding was being reported as water pooled near snow-clogged drains. At the same time, a third of an inch of ice covered most surfaces from Portage and Valparaiso in Indiana west to the Mississippi River. Numerous traffic accidents were reported. The Chicago Skyway had to be closed for salting after a multi-car pile-up occurred on the icy thoroughfare and accidents at I-88/I-294 intersection near Oak Brook resulted in injuries. An ice build-up on Willis Tower interfered with NOAA Weather Radio transmissions which emanate from the antenna array there. And at Portage Indiana, the ice accumulation at had reached 0.4 inches late Wednesday evening and there was concern power lines stressed by the ice and wind were at risk.
Weather troubles may only be beginning in the Chicago area--the next concern is flooding. Rainfalls of nearly 2 inches are predicted Thursday afternoon and night as temperatures rise above freezing. The melting snowpack, which contains 0.75 to as much as 3.25 inches of water, along with run-off from wind-driven downpours may send an unmanageable amount of water into area waterways inducing flooding.
Storm's grip on area to be a long one as system loops over Iowa in coming days
In a peculiar twist, computer models slow the massive storm's center over Iowa Friday and Saturday, rotating it in a circular manner over the state. This is to slow the storm's exit from the Midwest and means snow accumulations may grow extreme from sections of east and central Nebraska northeast into eastern South Dakota, northwest Iowa and Minnesota. Accumulations in hardest areas there may top 20 inches. Forecast models ultimately bring the cold pool of air above the storm eastward over Chicago this weekend and suggest significant snow accumulations aren't out of the question here. Early estimates suggest as much as 2 to 6 inches of snow may occur--though these figures must be viewed as preliminary and subject to update.
Dear Tom,
What is the average daily temperature at the South Pole?
Mel Dormer Aurora
Dear Mel,
The National Weather Service maintains the Amundsen-Scott weather station located directly at the South Pole at an altitude of 9355 feet. The "warmest" time of the year there is in January, when there is 24 hours of sunlight a day and the average daily temperature climbs to about minus 20. The coldest time of the year is in July's mid-winter darkness when typical readings register about minus 76.
Current weather from the Amundsen-Scott station is always available at http://weather.noaa.gov/weather/current/NZSP.html.
The weather station at Vostok, Antarctica takes the dubious honor for recording this planet's lowest temperature, a reading of minus 129 on July 21, 1983 while the record high there is just 7.5 degrees above zero reached on Dec. 27, 1978.
A mammoth winter storm, being described as a "once in a quarter century system" by forecasters in the Plains and western Midwest where concern is high a travel-crippling blizzard is about to hit, threatens significant icing in sections of the Chicago area away from Lake Michigan Wednesday night and early Thursday. Drenching rains are likely to follow as temperatures warm Thursday and Thursday night (Christmas Eve), a development all but assured to obliterate any chance for a White Christmas here this year. The combination of rain and rising temperatures is likely to melt the snow which fell Tuesday. Midway Airport's 3 inches was the site's heaviest this season while the official O'Hare tally had reached 2.4 inches late Tuesday evening. Even heavier amounts occurred to the west and north of the city-- among them 4.7 inches at Pecatonica (west of Rockford), 4.5 Carpentersville, 4.2 DeKalb, 3.8 at Rockford, 3.6 Oak Brook, 3.5 Downers Grove and 3.2 inches Mount Prospect. Snowfall extended into Indiana leaving 3.5" in Portage and 2" at Morroco.
The developing storm is already expansive--and it's to grow even larger in coming days. Its track is one likely to shunt the system's big snows well to the west of Chicago while promoting sleet and freezing rain development instead. The storm is predicted to wend its way from New Mexico across Oklahoma and Missouri, passing near Quincy, before continuing north into southern Minnesota where it is predicted to stall Saturday/Saturday night. This suggests the system's affect on Chicago could last through the coming weekend. A huge spread in pressure readings between the intensifying low pressure and a large Canadian high to the north is driving the strong winds whipping across the Chicago area Wednesday morning and likely to gust above 30 mph here in coming days.
Ice development isn't an everyday occurrence in Chicago and its suburbs. It occurs an average of 6 to 8 hours each season. Atmospheric conditions must be perfect. The powerful easterly winds blowing at ground level from Lake Huron into Chicago though a layer of sub-freezing air only 2,000 feet deep Wednesday are competing with moist air and warmer temperatures riding 50 m.p.h. winds up and over the chilly air. This set up is producing the patches of snow, ice pellets and light freezing rain in progress in the Chicago area Wednesday morning. Precipitation intensity is to increase later Wednesday and Wednesday night as incoming moisture increases. At full intensity, the storm threatens blizzard conditions--including snowfall measured in feet and 50+ mph winds---across sections of Nebraska, Iowa, Minnesota and Wisconsin likely by Thursday to bring travel to a halt. The storm is responsible for a potpourri of winter weather warnings across 23 states--including Illinois, Wisconsin, Indiana and Michigan.
Downpours and rising temperatures to wash away Chicago White Christmas prospects
Chicago may be in for equivalent of three-quarters of the city's December full month precipitation tally in coming days. 26 computer model projections of the water equivalent precipitation likely to fall here averages 1.78 inches--with individual forecasts ranging from a low of 0.84 to as 3.03 inches.
Dear Tom,
What are Chicago's temperature records for the holiday period from Christmas Eve into Jan. 1? We were wondering about the mildest and coldest.
Edna Polivka
Dear Edna,
Chicago's holiday temperature extremes are mighty extreme, but that's characteristic of the city's continental climate (so-called because our climate is typical of the conditions that prevail toward the interior of continent-sized land masses -- areas far removed from the moderating influences of oceans).
Chicago's Christmas Eve (Dec. 24) temperature records are 64 degrees (1889) and 25 below zero (1983); on Christmas Day (Dec. 25), 64 degrees (1982) and minus 17 (1983) -- back-to-back years!; New Year's Day (Jan.1), 65 degrees (1876) and 10 below (1969). The nine-day averages (Dec. 24 - Jan. 1) range from 41.9 degrees (1875-76), the mildest, to 2.7 degrees (1983-84), the coldest.
Snow greets morning commuters Tuesday and is likely to fall steadily through mid-morning, producing accumulations of 1 to 3" before tapering to sporadic flurries by midday. It marks the 8th time measurable snow has fallen here this season. The system responsible is an offshoot of a much larger winter storm under development to the west. That system has prompted advisories and watches for wintry weather across sections of 17 states -- as far east as northwest Illinois and western Wisconsin.
It is likely to bring the Plains and western Midwest rapidly deteriorating conditions Wednesday and Thursday as snow and increasing winds crescendo into full-blown blizzard conditions. The region has the potential of receiving more than a foot of snow by week's end -- and includes sections of Nebraska, South Dakota, western Iowa and Minnesota. A multi-state area to the east -- including northern Illinois, southern Wisconsin and northern Indiana -- may be subject to a cocktail of sleet, freezing rain and snow beginning later Wednesday and Wednesday night until comparatively mild, moisture-laden winds off the Gulf of Mexico switch precipitation to all liquid Thursday.
Big winds on the way to Chicago with the approaching storm
Powerful winds gusting above 35 mph will begin sweeping the Chicago area from the east on Wednesday. The flow off mid-30-degree Lake Michigan waters is likely to limit the extent of freezing precipitation in the city and areas of northeast Illinois and Wisconsin immediately adjacent to the lake. But in sections of the metro area -- i.e. the west and northwest suburbs -- which lack access to lake warming, computer models suggest 8 to 12 hours with an icy mix of sleet, freezing rain and snow Wednesday night and possibly the first hours of Thursday.
Though a period of snow or mixed snow and sleet may occur on the front end of the wintry onslaught late Wednesday and Wednesday night, the presence of a layer of warm air aloft is to shut down the formation of the ice crystals which seed snowflakes, shifting precipitation to a mix of super-cooled water droplets -- consisting of liquid which is below freezing but freezes upon contact with cold outdoor surfaces -- and ice pellets. Such a set-up would be a recipe for some harrowing travel conditions away from the warmth of the lake and city Wednesday night.
Computer models suggest the water content of precipitation expected to fall in Chicago's between Wednesday and Christmas is to exceed 1.50" -- much of it to fall in some wind-driven downpours Thursday. By Christmas Day (Friday), the northeast-bound storm, expected to track well west of Chicago, should whip much colder air around its south flank and the metro area on howling southwest winds. Daytime temperatures are to tumble and are unlikely to emerge from the 20s this weekend.
Freezing rain occurs in Chicago an average of 6 to 8 hours a year
Freezing rain, while not a common phenomenon in Chicago, is not stranger either. Studies have shown the city can expect a period of freezing rain lasting 6 to 8 hours at some point in most cold seasons.
Dear Tom,
What is the record snowfall rate for Chicago?
Marty Shanahan, Plainfield
Dear Marty,
On the evening of Feb. 23, 1967, less than a month after the city's 23-inch "Big Snow", Chicago was hit by a full-scale blizzard. Traffic came to a standstill as blinding snowfall reduced the visibility to zero, stranding thousands of motorists. According to Chicago climatologist Frank Wachowski the storm dropped 3.5 inches of snow at Midway Airport in just one hour, a city record. The intense storm that brought up to 6 inches of snow to the metropolitan area in just a few hours was accompanied by considerable thunder and lightning and temperatures in the teens. The snow was blown horizontally and piled into huge drifts by northwest winds that gusted to 47 mph in the city and as high as 82 mph at Ogden Dunes in northwest Indiana.
The week ahead promises to be cloudy with frequent bouts of precipitation. After a dusting of snow Sunday night, some light snow will return on Tuesday as a weak weather disturbance passes through the Midwest. The next system, slated to move into the southern Plains on Wednesday, is stronger with the potential to become a major storm that could disrupt holiday travel in the Midwest. Current forecasts bring the storm close to Chicago on Christmas Eve, allowing a surge of warmer air to cause much of the precipitation here to fall as rain or a wintry mix. Colder air would sweep back into the area early Christmas morning, changing the precipitation back to snow with some accumulation possible especially in areas west and north of the city. Any southward shift in this track could increase the snow threat here, so the storm's final outcome is still in question.
The East digs out
The monster blizzard has ended in the Northeast, leaving record snowfall in many areas. Widespread snow totals in excess of 2 feet were common from western North Carolina to southeast New York. One of the heaviest totals was 26.3 inches at Upton, N.Y., on eastern Long Island.
Dear Tom,
The huge snow totals from the storm in the East remind me of Chicago's paralyzing snowstorms in 1967 and 1979. Are we overdue for another?
Kate Flaherty, Lisle
Dear Kate,
Huge snowstorms are really quite rare in Chicago with only three on the books that totaled more than 20 inches in 125 years of weather records dating back to 1884. You have referred to two of them, the 23.0 inch "Big Snow" of Jan. 26-27, 1967, and the "Blizzard of '79" that brought 20.3 inches on Jan. 12-14, 1979. The city's only other 20-inch-plus storm took place nearly 11 years ago on Jan. 1-3, 1999, when a monster storm dropped 21.6 inches of snow on the Chicago area. Most of Chicago's big snowstorms generally bring about a foot of snow, and typically the city gets a storm of that magnitude about once every six years.
Snow fell across the Chicago area Friday night and Saturday with total accumulations up to 4 inches in colder northwest suburban areas, including Palatine and Arlington Heights, while in areas from the city south and east the snow was mixed with rain keeping totals in the 1-2 inch range. After some lake effect snow showers shift east into northwest Indiana early Sunday, the city awaits the arrival of a fast-moving Alberta Clipper expected to bring 1-2 inches of snow beginning Sunday afternoon.
Christmas Eve storm bears watching
Of greater concern is a storm system forecast to arrive Christmas Eve. With access to Gulf moisture the storm promises to be a prolific snow producer. Chicago will once again be on the cusp between rain and snow with the latest forecast track favoring snow for areas west and north of the city and a mix of rain and snow from the city south. Colder air will filter in on Christmas, bringing snow and snow showers much of the day.
East Coast buried
The mammoth snowstorm paralyzing the East will finally be winding down Sunday leaving a legacy of widespread 1 to 2-foot snow totals from western North Carolina to southern New England.
Dear Tom,
I just read your recent column about the snowy December 1951. Didn't the opening of the Edens Expressway take place in a major snowstorm about that time?
Howard Mason
Dear Howard,
The official opening of the Edens Expressway took place Dec. 20, 1951, during a major snowstorm that brought Chicago a three-day snow total of 7.3 inches. At 11 a.m. that day, the ribbon was cut near the overpass at Peterson and Caldwell avenues, which marked the south end of the new six-lane expressway. A dozen snowplows ran interference as a motorcade traveled 14 miles north along the highway to its northern limit at Lake-Cook Road. One of the ribbon cutters was William G. Edens, after whom the highway was named. He was a pioneer in promoting the state's first highways in 1918.
A snowstorm of historic proportions is burying a wide swath of the Mid-Atlantic under as much as 1 to 3 feet of snow as the weekend gets underway. The Washington D.C. area is to end up among the locations hardest hit with as much as 20 inches of snow a possibility -- the heaviest accumulation to hit the nation's capital in at least six years and enough to grant the windy, rapidly intensifying system a spot among that city's Top 3 biggest snowstorms. Washington snow records date back to 1885.
Moderate snow had commenced there late Friday evening and computer projections indicated the storm could end up generating nearly 3" of water-equivalent precipitation before exiting early Sunday -- enough moisture to conceivably fluff up into 18 to 29" of snow. The northeast-bound snowstorm has Philadelphia, Atlantic City, New York and Boston in its sights where it threatens to deposit a traffic-crippling thick cover of wind-driven snow. Coastal wind gusts may top 60 mph as the system's central pressure crashes to 976 mb (28.82") off the Mid-Atlantic Coast. The storm's intensification is being driven in part by its ability to tap energy from the Gulf Stream -- the warm current of water which flows from the Florida Straits north to the UK and northern Europe. It has provided a fertile breeding ground for many of the Eastern Seaboard's most intense storms.
By late Friday, 16" had fallen in Boone and 15" at West Asheville -- both in North Carolina -- with 13" down at Bluefield, Va., and 6" at Pineville, Ky. In the storm's warm sector, South Carolina coastal rains Thursday included 5.38" at Mt. Pleasant and 3.93" at Charleston.
There's a connection between Chicago's Saturday snow and the mammoth eastern storm system. The north/northeast winds traveling into the city off Lake Michigan are occurring beneath the deepening storm's western flank, tapping colder air. The process destabilizes the atmosphere by increasing the rate at which temperatures drop with height. Air rises and cools when this occurs -- transforming lake moisture into clouds and snow. Just how much lake enhancement of snowfall occurs will dictate the final tallies across the Chicago area's lakeside counties. What's more, a second period of snow showers could lay down a quick 1-2" late Sunday into Sunday night as an Alberta Clipper sweeps into the Midwest.
The potential for a more significant winter storm system coming together across the nation's mid-section later this coming week grew stronger Friday. Computer models, far from unanimous on storm development only several days ago, now suggest a vigorous system is likely to come together mid and late next week. While the track this storm takes is far from settled, a growing number of forecasts had the system following a more southerly track between Wednesday and Friday (Christmas Day). This increases the possibility snow with the system may occur much closer to -- if not over -- at least sections of the Chicago area. This will have to be monitored.
Valdez, Alaska, hit by near-record 6.5 feet of snow past 5 days
With all the snow in the Lower 48, it should be noted the port city of Valdez in southern Alaska has been hit with one of its heaviest weekly snow tallies ever. Snow began falling Monday and by Wednesday had totaled 68 inches -- nearly 6 feet. Additional spells of snow boost had boosted tallies to 6.5 feet as Friday ended.
Dear Tom,
A recent column talked about all the snow in December 2000. Wasn't the rest of that winter relatively snow free?
Richard Strombom, Wheeling
Dear Richard,
You are absolutely correct. After the city was staggered by one of the snowiest months on record in December 2000, the rest of the winter turned out to be a piece of cake. More than three-quarters of the season's snowfall fell that month. At Midway Airport, where December brought a record 41.3 inches of snow, the rest of the winter delivered only 13.2 inches, bringing the final total for the season to 54.5 inches. January recorded just 2 inches, February 2.9, March 6.6 inches and April a meager 0.6 inches. At O'Hare, December snowfall tallied 30.9 inches and comprised nearly 80 percent of the city's official 39.2-inch seasonal total.
The season's most powerful storm to affect the East Coast--potentially the most prolific snow producing system to sweep the mid-Atlantic including the Nation's Capital in years---is lifting out of the Gulf of Mexico Friday morning. It's expected to deal the heavily populated East Coast corridor from Washington DC to Philadelphia, New York and Boston a major blow producing snowfalls measured in feet at the hardest hit locations. Howling winds with the rapidly intensifying storm threaten to combine with the huge accumulations to cripple travel in the area.
Full season snow totals in Washington DC the past three years have ranged from 4.9 inches to as much as 9.5 inches. With more than a foot of snow a distinct possibility there between the onset of snowfall Friday night and its conclusion Sunday morning, the approaching storm threatens to produce more snow than any of past three full snow seasons.
Tropical moisture being drawn into the ominous storm drenched sections of Florida and the Gulf Coast Thursday. A spotter west Port St.Lucie in east-central Florida reported 12.13 inches of rain--6 inches of which fell in 90 minutes. Rainfalls of 4.35 inches hit Miami with 3.96 inches reported at Pompano Beach and 3 inches at Key Biscayne. Abbeville, Louisiana was drenched by 2.38 inches while Baton Rouge recorded 1.90.
Computer models Thursday began shifting the developing storm's track closer to the East Coast than initially predicted. Explosive intensification was also indicated in the updated projections. The system's central barometric pressure is predicted to drop to 976 mb. (28.82 inches) as it reaches coastal Atlantic waters off southern New Jersey late Saturday night, indicating a system capable of powerful winds and embedded thundersnow.
Chicago facing weekend snows too--first to stick in 10 days
Though hardly in the same league as the Eastern snow system, Chicago appears to be facing accumulating snow this weekend as well. Above freezing temperatures and limited precipitation coverage Friday mean any precipitation which falls is likely to occur as liquid or a few ice pellets or flurries with little or no accumulation. It's Friday night, as cooling takes place aloft and amid gradually strengthening northeast ground-level winds, that spotty light evening precipitation is to build into more general snowfall which may accumulate. Snow is to continue at times Saturday into Saturday night, possibly---with vertical temperature declines supporting some lake moisture-enhancing precipitation modestly here---the early read on potential accumulations suggests possible 2 to 4 inches accumulations. Just how much lake moisture ends up getting into the disturbance is likely to dictate ultimate accumulations in lakeside areas.
A southeast-bound Alberta Clipper may ratchet snowfall up again Sunday afternoon into the night after a morning of flurries.
Winter running warmer and less snowy than year ago
December temperatures are running 3-degrees below normal this year----but almost 4-degrees above a year ago. Snowfall continues at less than half last season's pace.
Dear Tom,
We get big snows that last a day or two, but sometimes it snows just a little bit for days on end. What is Chicago's record for the largest number of consecutive days with snow?
Todd Pierce
Dear Todd
Your observation that Chicago's largest snow storms are usually just one-day or two-day events is correct. In 125 years of snowfall records dating from the winter of 1884-85, Chicago's all-time greatest snow storm was the blizzard of Jan. 26-27, 1967, when 23.0 inches of wind-whipped snow (and 6-foot drifts) brought the city to a standstill.
However, a scan of Chicago's snowfall data also supports your contention that periods of "little snows" and flurries can sometimes go on for days. In that regard, Chicago's extreme event was the nine-day period of Jan. 29 through Feb. 6, 1902. Measurable snow fell on each of those days, but the 9-day total was only 5.0 inches.
Snow in Chicago is running at less than half the pace of a year ago. 13.9 inches was on the books on this date a year ago--but the 2009-10 snow season has seen just 6.5-inches--47 percent (less than half) as much. It's a trend which may change in the weeks ahead starting with a weather system expected to produce some sticking snow late this week and into the coming weekend. While not a huge system, computer models, which produce their initial estimates of precipitation in terms of the amount of liquid a given disturbance may generate, put about a quarter inch of moisture down across the Chicago area. Much of that is predicted to fall Friday night into Saturday night. Temperatures predicted through the atmosphere as that happens appear likely to be cold enough to support snowflake formation in approximately a 13 to 1 snow-to-water ratio. In such a set-up the 0.26 inches of liquid this system could produce up to 3 inches of snow over parts of the Chicago area, according to very preliminary estimates.
The one wildcard with the Friday night/Saturday disturbance is the amount of moisture northeast winds off Lake Michigan may contribute to the system's snowfall as temperatures above the ground cool. This could boost snow totals in areas of northeast Illinois and southeast Wisconsin west of Lake Michigan. Precipitation appears likely to end later Saturday night in all but sections of the Indiana snowbelt. But another disturbance slated to arrive Sunday afternoon and evening may initiate yet another round of snow or snow showers. Arctic air follows Monday into Tuesday before a potentially more important storm system lifts into the Midwest from the Plains mid-week.
White Christmas chances rising
Approximately four in ten Christmases have had an inch or more of snow on the ground since records began here in 1884--yielding a 40 percent historic probability of a White Christmas. If the Wednesday/Thursday system becomes a reality next week, the odds for a white Christmas 2009 may be higher.
Frigid arctic air on hiatus here the next two days
Temperatures are in a rebound mode here the next two days. The respite from the arctic chill of recent days is to include the return of above freezing daytime highs over much of the area. The 38-degree reading predicted Thursday afternoon would be a 15-degree increase over Wednesday's 23.
Dear Tom,
What is the most snow we've ever had on Christmas Eve and Christmas Day?
Ellen Abbott Oak Park
Dear Ellen,
While snow on the ground Christmas Day is picturesque and idyllic, a Christmas snowstorm can be a nightmare. Such was the case back in the very snowy December of 1951, when the city was hit by a major holiday snowstorm that began late in the afternoon of Christmas Eve and ended just before noon Christmas Day, bringing an official snowfall of 8.6 inches. The city had been hit by three other snowstorms in the days leading up to Christmas and combined with this storm nearly halted holiday travel. The two-day storm dumped 4.6 inches of snow on Dec. 24 and the final 4.0 inches on Dec. 25. Chicago has recorded two snowier Christmas Days; 5.1 inches just one year earlier in 1950 and 5.0 inches in1909.
Air roaring out of Montana's mountains produced eye-catching 50-degree 24-hour temperature increases Tuesday. The milder air is eastbound and expected to go to work on Chicago's arctic chill in coming days. Down-sloping Chinook winds were behind Montana's surging temperatures, compressing and warming dramatically upon reaching the higher pressures at the base of the state's mountains. Chinook warming is often stunning and one reason the largest U.S. short-term temperature swings have historically occurred in the region.
In the space of 24 hours, residents of Great Falls, Mont., which had shivered Monday in the same frigid arctic air mass which grips Chicago as Wednesday gets underway, watched temperatures surge from Monday's bitterly cold -12-degree high to Tuesday's dramatically milder 39 degrees. The eastbound mild air, while unlikely to warm the Chicago area as dramatically, is still expected to push readings here above freezing Thursday and to near freezing Friday before temperatures trend lower over the coming weekend. And there are some early signs--not yet carved in stone but worth monitoring--that December, which passes the halfway point Wednesday, could feature an arctic blast at the 1 to 2 week range.
A huge pool of westward-drifting, unseasonably mild air taking shape over Greenland and northeast Canada is to force a pool of cold air north of the Great Lakes to sink southwestward into the Midwest this weekend. The steepening rate at which temperatures fall with height as this takes place toward the weekend sets the stage for cloud and snow shower development Friday. Northeast winds sweeping off Lake Michigan's comparatively mild ice-free waters may enhance that snowfall. It wouldn't be surprising to see some accumulation in the Friday/Saturday time frame as this occurs.
A powerful batch of jet stream winds -- a so-called jet streak -- rides into the Midwest later Monday and Tuesday. Such features encourage air to rise, producing clouds and precipitation. With several additional jet streaks slated into the Midwest next week as a new batch of frigid arctic air gathers to the north, the potential for a White Christmas here appears to be increasing. Meteorologists define a White Christmas as any Dec. 25 with at least an inch of snow on the ground.
Stunning 20"+ December rain tallies on Gulf Coast an El Nino by-product
New Orleans was drenched by more than 5" of rain Monday and Tuesday bringing the city's December rain tally to 22.47 inches. Wettest of all in the New Orleans area is Marrero with a 26.52" tally in only the first 15 days of the month.
The wet pattern appears related to El Nino. December rainfalls are running well above normal from Houston (3.85") to Mobile, Ala., (12.70"); Tallahassee (8.65") and Jacksonville (5.25") -- both in Florida; and east and north across Atlanta (4.65") and Charleston, S.C. (5.84"). Wet cold seasons and more numerous severe weather outbreaks are all attributes of El Nino periods there.
Dear Mr. Skilling,
How are icebergs formed and how many are there?
Alice Van Rosendale, South Holland
Dear Alice,
Icebergs -- thousands per year -- are composed of freshwater ice that was formed over land and eventually makes its way into the sea. This occurs in two ways. In the Northern Hemisphere, icebergs are born when glaciers terminate at the ocean and pieces break away (calve) from the parent glacier. Around Antarctica, the continental icecap in places extends out over the ocean as an ice shelf, and huge pieces occasionally break off.
In describing icebergs, The Greenland Tourism Bureau says their "... magnificence and majesty cannot adequately be captured on film -- they must be experienced firsthand! ... It also gives food for thought that icebergs were originally created in a slow transformation from snowflakes to ice during a period predating modern history."
Arctic air is back in control Tuesday, riding biting northwest winds into the area. The invasion of cold air is to outpace solar heating. The sunshine expected to follow daybreak flurries isn't likely to produce typical daytime heating because the cold air is flooding into the area faster than the sun can warm it. The presence of a heavy, reflective snowpack to Chicago's west is only expected to intensify Tuesday's chill. Temperatures are to continue on a downward trajectory ending up in the 10 to 15-degree range as wind chills lower to single digits by and during the afternoon.
Predictions last week that the season's lowest values of a key cold weather indicator -- the Arctic Oscillation Index -- proved the first clue an arctic air mass of impressive intensity was likely to take shape over Canada. It has; the prediction was dead on. The season's largest and coldest mass of air to date has come together in recent days over most of the western two thirds of Canada and oozed south into the Plains and Midwest. Low temperatures in the recent mornings have plummeted to -20 to -45 degrees from Ontario Province and Hudson Bay westward -- but nowhere has it been colder than in sections of Alberta, British Columbia and Saskatchewan Provinces. Edmonton, Canada, has been at the epicenter of the cold air, registering readings so cold in recent mornings air traffic has been impacted. Sunday morning's record shattering -51-degree low was accompanied by winds which lowered chill readings to -73. Monday morning wasn't much better: the -44-degree low fell just shy of record status but was 45 degrees below the "normal" early December low of 1 above. Cold as Sunday's -51-degree minimum was, it fell 4 degrees short of Edmonton's all time low of -55 recorded Jan. 26, 1972.
El Nino cold seasons often include arctic outbreaks and snow -- just fewer of them
A number of you have written asking whether chilly air's recent appearance is indicative of the demise of El Nino. Not at all. El Nino conditions are alive and well in the equatorial Pacific and there are clear signs of their impact in the driving rains noted in the Gulf Coast region in recent days. The moderate El Nino now in progress may strengthen further.
Some have gleaned from our discussions of El Nino that arctic air and accumulating snow are "no-shows" in El Nino cold seasons. Nothing could be further from the truth. What is true is that two-thirds of El Nino cold seasons see fewer arctic outbreaks and less snow. As had been noted -- and seems to be the case this year -- the tendency for ridging aloft over Greenland and northeast Canada, unrelated to El Nino -- often signals cold weather for the Midwest and Chicago. In periods when this happens, cold air tends to pour into the U.S. from Canada.
It's been our sense right along that Chicago's cold season was likely to flip-flop from periods of arctic cold air related to the Greenland blocking to periods of El Nino-enhanced warming. An interval of such warming is to send temperatures above freezing Thursday. But, strong ridging predicted over Greenland and northeast Canada is to force cold air into Chicago this weekend.
Don't write off chance for a White Christmas in Chicago
Every recent run of the National Weather Service's 16-day Global Forecast System (GFS) model suggests measurable snow may fall in the coming two weeks. That's a development which indicates it's too early to write off prospects for a white Christmas here. Ninety-nine percent of the past 125 years have seen snow in Chicago between Dec. 15 and Dec. 25; 66 percent see an inch or more; and 34 percent include 3 inches or more. Meteorologists define a White Christmas as any which includes an inch or more of snow on the ground Dec. 25.
Dear Tom,
How many days in the year do we receive snow in Chicago? I'll estimate about 25 days.
Robert Browning, Chicago
Dear Robert,
"Snow days" can be tallied in two ways, but your estimate is low either way: Snow flies surprisingly frequently around here. That's good news or bad news, depending upon your point of view.
The National Weather Service defines two kinds of days with snow: those with measurable snow (an accumulation of one-tenth inch or more on grassy surfaces) and those with mere "traces" (flakes in the air, but no accumulation).
A computer sweep of 80 years (1929-2008) of Midway Airport snow data, courtesy of Chicago weather guru Frank Wachowski, yields these surprising numbers: On average, we experience 30 days per year with measurable snow and another 34 days with traces, for an annual total of 64 snow days.
As a low pressure system approaches northeast Illinois, clouds thicken and scattered light showers are expected to break out Monday. Best chance of showers will be in northern sections of the metro area. The most significant impact from the low is expected to occur across Minnesota and northern Wisconsin, where up to 5 inches of new snow could accumulate Monday. Colder air will follow the front with strong northwest winds flowing over warmer southern Lake Michigan waters, triggering snow showers over northern Indiana and the southwest lower Michigan snow belt Tuesday. Temperatures moderate briefly Thursday before another cool-down next weekend.
Flooding along the Gulf Coast
A stationary front oriented west-east just south of the Gulf of Mexico coastline has dumped heavy rains over the southern portions of Louisiana, Mississippi and Alabama, causing widespread flooding. New Orleans reported rainfall of 5 to 7 inches Sunday. Another wave of heavy rains is expected to dump an additional 2 to 4 inches over that same area Monday and Tuesday. Dense fog has also seriously impacted driving conditions all along the Gulf coastline from Texas to the Florida panhandle.
Dear Tom,
I am impressed by the fabulous graphics in your weathercasts and the magnificent colors that are used to illustrate the buildings in downtown Chicago, especially the bright red skyscraper. Are the colors real, or are they just presented to represent the various landscapes of your city?
Leigh Rainey
Dear Leigh,
The colors are real. We receive occasional questions about Chicago's unique skyline and, in particular, that imposing red structure. Because of its massive height and bright red color, the CNA Plaza Building is one of the more prominent buildings on Chicago's downtown skyline.
Rising to 601 feet and 44 stories, the CNA Plaza Building was completed in 1972 and is located at 325 S. Wabash Ave. And yes, that is the structure's actual color. It is bright red, and red figures in many interior fixtures of the building as well.
Several sections of the metro area and far suburbs may have some slick spots to start this Sunday morning. A mix of rain and spotty sleet and snow spread into northeast Illinois and northwest Indiana Saturday evening, and was expected to diminish and end sometime after midnight. The precipitation started out as rain, but because the air was extremely dry, especially in northwest Indiana, a process called evaporative cooling took place as the raindrops fell through the very dry air, dropping air temperatures below freezing and resulting in a wintry mix of precipitation. It could be slick in some spots early this morning -- even without precipitation -- wherever surface temperatures remain at or below 32 degrees.
Next surge of cold air hits Tuesday
Southerly winds, high temperatures in the upper 30s and rain on Monday will work on melting the remaining snow cover deposited by last week's storm. But a southward shift in the polar jet stream will swing winds aloft around to the northwest, allowing a surge of cold air out of the Canadian Tundra to flow into the Midwest and and western Great Lakes Tuesday. After Monday, Chicago's high temperatures will probably not climb out of the 20s again until Thursday.
Dear Tom,
You have described December as a winter month, but in my experience here in Chicago it seems that it is a month of tremendous temperature variations with extreme cold but also surprising warmth. Am I off base?
David Witherspoon
Dear David,
Your description of December temperatures is apt. The month is decidedly wintry on balance, but it's a testament to the variability of Chicago's continental climate that huge temperature swings occur routinely in December. December's all-time temperature extremes span a range of 96 degrees, from 71 degrees (Dec. 3, 1970, and again on Dec 2, 1982) to 25 below zero (Dec. 24, 1983).
That's bad enough, but consider this: In a normal December, the highest temperature in the month will be 55 degrees, and the lowest will be 0 degrees. A normal December produces very mild and very cold temperatures.
Icy weather threatens sections of the Chicago area late Saturday night and into Sunday morning as Gulf moisture sweeps in with haze, fog, widespread low cloudiness and -- most ominous of all -- possible freezing rain and/or sleet. Computer models are predicting a quarter to a third of an inch of liquid precipitation, suggesting it may fall into a subfreezing layer of air later Saturday night into Sunday morning. It's a development which threatens icing in some locations -- particularly in colder inland areas still covered by snow in the wake of the windy midweek storm.
But before any iciness arrives, arctic air is to loosen its grip on this area's weather through early next week. Saturday's predicted highs in the mid to upper 30s represent a 15-degree temperature increase over Friday's levels. The cold air's exodus is being driven a rearrangement of jet stream winds across North America. The powerful polar jet, which first dipped into the Chicago area late this week, channeling frigid air from North America's northernmost reaches, is to lift north, taking the harshest chill with it.
While sunshine should be in good supply a portion of Saturday, northbound Gulf moisture will begin to saturate the atmosphere later today and into Saturday night, producing low clouds, haze and a cold rain possibly mixed with ice pellets. It's at that point Chicago meteorological set-up becomes dicey. The normal nighttime pullback in temperature readings -- though less than in recent nights -- may still be enough to allow readings to dip to freezing or below. That means rain or a rain/sleet/flurry mix Saturday night is likely to fall into a chilly layer of air hugging the ground. Enough rain is to fall to potentially create some dangerous icing where temperatures are at or below freezing.
Despite recent cold blast, this December running 4+-degrees ahead of last
December 2009 is running colder than normal to date. Its mean temperature of 27.4 degrees is 4.2 degrees below the long-term average. Six of the month's opening 11 days have produced temperatures below normal. The opening week and a half of this month ranks among the coldest 15% of such periods in 139 years of record keeping.
A buckling jet stream next week on Tuesday and Wednesday is to latch onto another lobe of frigid arctic air and drag it into the U.S. And key cold weather indexes -- among them the Arctic Oscillation Index (AO) and North Atlantic Oscillation Index (NAO) -- suggest waves of cold air may continue to reach the Midwest through at least mid-month. What's more, a pool of warm air aloft over Greenland threatens a return of the blocking pattern responsible for so much of the cold weather which dominated the last two winters here.
Dear Tom,
The blizzard this week missed Chicago but it makes me curious as to the differences, if any, between a blizzard and a snow storm. Those terms are always being tossed around, but there must be a difference. Am I being picky?
Jeff Weiss, Chicago
Dear Jeff,
Meteorological jargon often finds its way into general use, but the precise definitions of terms sometimes get lost in the shuffle of news reports and commentary. You're not being picky. Meteorologically, the distinctions between a snow storm and a blizzard are significant.
A snow storm is a generic term for any storm with lots of new snow, whereas a blizzard is a special and rather rare event: a severe storm that brings sustained winds of 35 mph or higher and sufficient falling and/or blowing snow to reduce visibility to less than 1/4 mile for at least three hours. New snow is not a necessary blizzard criterion.
The season's first blast of truly frigid arctic air sent Chicago temperatures tumbling Thursday to 0-degrees for the first time this season. The reading at O'Hare was nearly three weeks ahead of the average first date for cold air of that intensity. Over the past 139 years, Chicago's first zero has occurred on or about Dec. 29--though the most recent 11 years have seen 0-degree temperatures arrive closer to Jan. 7---a full week later. Thursday's coldest daybreak readings occurred across the northwest and western suburbs where more snow was on the ground in the wake of Wednesday's windy snowstorm. Snow has a cooling effect. During the day, snow is known to reflect nearly 90 percent of incoming sunlight back into space--a property known as its ALBEDO. Temps struggle to warm over high albedo surfaces like snow as compared to bare ground, which absorbs incoming sunlight and warms. It was easy to see the process at work Thursday as temperatures in the snow-covered northwest suburbs remained in single digits.
The morning began with the coldest inland locations reporting sub-zero readings, including 5-below in Island Lake in far western Lake County, Ill., 4-below at DeKalb and South Elgin, 3-below at Aurora and 2-below at Rockford.
The chill was so extreme that ice-free water bodies appeared to produce steam. In reality, the "steam" was ice crystals leaving the water surface in a process known as SUBLIMATION. Sublimation occurs when a liquid changes phase, moving directly from its liquid state to a solid state--in Thursday's case moving from water to ice crystals.
Darkness at the top of the world sets the stage for winter's chill
The sun never rises this time of year over the northernmost sections of North America. It's a development which allows the rapid accumulation of cold air in the arctic. Then, as fall and winter storms produce a snowpack, the chill is able to advance farther and farther south with the snow reflecting sunlight which would otherwise warm the air away. The presence of a cover of snow combined with weak sunlight this time of the year makes us vulnerable to arctic outbreaks. Sunshine in December delivers just 21 percent of the energy found in summer sunlight.
South Florida enjoys record warmth, Miami ties all time December record
While chilly air covered the nation nearly from coast to coast, south Florida basked in record breaking temperatures. Record highs occurred in West Palm Beach (87-degrees), Vero Beach (85-degrees), Ft. Lauderdale (87-degrees) and Key West (84-degrees). Miami's 89-degree high was not only a record for the date, it tied the highest temperature ever recorded there in December.
Blizzard conditions across the lake
The frigid air which had Chicagoans shivering activated the lake snow machine as is made contact with Lake Michigan's comparatively "warm" waters. Up to 10-inches of fluffy lake-effect snow fell near Kalamazoo while 7 inches was reported at Benton Harbor. The snow was sent airborne by 30 mph gusts.
Dear Tom,
In 1982 I remember a very warm Christmas, then one so cold a few years later that people were afraid to shut off their cars for fear they wouldn't start. Did these both set records?
Sharon Tamura, Chicago
Dear Sharon,
You are recalling Chicago's two most memorable Christmases (in a meteorological sense) and they actually occurred back-to-back. Christmas 1982 was the city's warmest on record in an El Nino influenced winter. The maximum temperature reached a balmy record high of 64 degrees on a Christmas so mild that many people were wearing shorts and washing their cars. The very next year the bottom dropped out of the thermometer, as the mercury plunged to a record low of minus 25 on Christmas Eve, followed by the city's all-time coldest Christmas with a high of just minus 5 and a low of minus 17.
It's a rare storm which generates a central barometric pressure below 29.00 inches of mercury (982 mb). Yet, that's precisely what happened to the amazement of many long time barometer observers here early Wednesday as the center the day's expansive storm moved over Chicago. Barometers, instruments which measure air pressures, registered readings which plunged to 28.91 inches (979 mb) between 7 and 8 a.m. Wednesday morning---the city's lowest atmospheric pressure reading in nearly 20 years. A storm must lift air at a tremendous rate and on a gargantuan scale to produce a reading THAT low--and yesterday's storm was doing all that and more. The blizzard it produced spanned sections of 7 states, burying an area from northern Kansas through Wisconsin and Michigan beneath snows of more than a foot. Howling winds in the snow band piled drifts 3 to 6 feet high. Its big snows extended into northwest Illinois where Freeport recorded 15 inches. Area's as close to Chicago as Beloit, on the Wisconsin border north of Rockford, was hit by 13 inches while northwest suburban McHenry County exceeded 8 inches. Hardest hit of all was the Madison, Wisconsin area where the heaviest snowfalls approached 19 inches. McFarland, Wisconsin topped the list at 18.9 inches while 18 inches was recorded on Madison's southwest side. The city's official tally reached 14.1 inches at the airport making it the 6th heaviest snowstorm to hit the Capital City since records began in 1948 . It was the heaviest snow in nearly two years there.
Chicago' snow tallies between Tuesday and Wednesday came to 3.1 inches at Midway and 4.2 at O'Hare. Downpours and above freezing temperatures Wednesday morning, melted much of the system's snow before light snows riding howling winds which gusted above 50 mph at some locations built into heavier snow showers, dropping visibilities to a quarter mile during the evening rush hour while depositing 1-2 inch accumulations.
Temperatures tumble to their lowest levels of the season---the coldest here in 10 months
Wind chill advisories greet northwest suburban residents as Thursday gets underway. Chills as low as -15 to 20-degrees were predicted to make the day's open the harshest of the young meteorological winter season. Fewer than half (44 percent) of all years have produced single digit lows this early in the season.
The air mass behind the windy cold wave kept temperatures at some northern Plains and northwest Midwest locations from rising above zero Wednesday---among them Hallock, MN where the high was -11-degrees and the low -22-degrees. Devil's Lake, ND recorded extremes of -8 and -20-degrees. But coldest of all were some higher elevation locations in Wyoming and Montana. An area near Tensleep, Wyoming began Wednesday at -38-degrees while an observer close to Dunkirk, Montana reported a -35-degree low.
Dear Tom,
What are the city's snowfall extremes for month of December?
Nick Recchia River Grove
Dear Nick,
After some teaser light snows in November, December typically marks the real start of Chicago's snow season, with the monthly total currently averaging in the 9-10 inch range. Since snowfall records began in 1884, the city has never recorded a snow-free December, though two years (1889 and 1912) came close, each receiving just a trace of snow---an amount too small to measure). On the high side of the snow ledger, the city's snowiest December was just nine years ago (December of 2000) when the weather observation site at Midway Airport logged 41.3 inches (although the official station at O'Hare received less).
Last winter, Chicago got 21.9 inches of snow in December.
Chicagoans haven't had to deal with an arctic outbreak of this intensity since last February. In what is sure to be the season's most jarring temperature downturn to date, readings are to dive unceremoniously toward Wednesday night lows in single digits and to do so amid snow showers riding roaring west winds through the area at up to 45 mph. Recovery Thursday will be limited with highs only making it into the teens.
Storms as powerful as Wednesday's are the product of extraordinary temperature variations. Readings across the nation Tuesday ranged from 85 at Kendall, Fla., to -35 below at Havre, Mont. -- an amazing 120-degree spread! It's little wonder the storm has become as intense or as expansive as it has. Sections of 36 states -- from Colorado to Maine -- were under a variety of winter weather advisories late Tuesday. Computer projections put the system's central pressure as it crosses Chicago Wednesday morning at 980 mb (28.93") -- placing the storm in rare company as one of the more intense systems to sweep through the city. That reading equals the central pressure of the infamous Edmund Fitzgerald storm at its height in November 1975. Pressures only reach such levels when the upward vertical motion of air at the heart of the system is extreme. Air rushing in from the storm's periphery to replace that ascending air is what leads to the powerful winds sweeping the Chicago area with gusts topping 45 mph at times Wednesday.
Storm's all but shuts McHenry County travel down
While precipitation trended to rain in Chicago late Tuesday evening after bursts of snow and sleet which greeted homebound commuters, travel across far northwest suburban McHenry County all but came to a halt as snow accumulations grew to 6.5" at Bull Valley; 6" at Algonquin and Harvard; and 5.3 at Crystal Lake by late evening. Other west and northwest suburban snow tallies included 8.3" at Ogle County's Leaf River, 6.5" at Belvidere, 6" at Rockford,5.5" at De Kalb, 4" at Mt. Prospect and Gurnee and 3.6" at Elk Grove Village -- and the storm is to generate additional snow showers in Wednesday's high winds totaling 1-3". A flood of milder air into the area helped fuel several thunderstorms from which sleet and snow fell. The lightning produced by one in Kane County's Elburn Tuesday was characterized as frequent.
Snowfalls to hit 1 foot in northwest Illinois near the Mississippi River
Bad as things were in Chicago's northwest suburbs, conditions were far worse in western Illinois where snowfall, whipped by powerful winds, headed for a foot. Visibilities across Iowa dropped to near zero in blizzard conditions. Des Moines had been buried beneath a foot of snow by evening -- and it was still snowing. In Lincoln, Neb., strong winds whipped heavy snow into 3 to 4 foot drifts.
Dear Tom,
I often hear meteorologists say it's "unseasonably hot" in the summer or "unseasonably cold" in the winter. That's not correct is it?
Kirk Melhuish
Dear Kirk,
No it's not, unless the adjective was intended to be "unreasonably". Extremes of heat in the summer and cold in the winter are best described by qualifiers such as extremely, unusually, torrid or bitterly -- but not by unseasonably, which literally means out of season. In Chicago, a 70-degree day in January would qualify as unseasonably warm or mild as would a July day in the 40s best be described as unseasonably cold or chilly. When Chicago dropped to -27 degrees on Jan. 20, 1985, meteorologists used terms like "all-time record cold" or "cold as it's ever been" to describe the event.
The season's most potent storm to date may bring sections of the Chicago area the biggest snowfall in 10 months. Snows, expected to mix with sleet and even some rain before diminishing later tonight, could accumulate to as much as 3-7 inches before that happens across the city and close-in suburbs. Even heavier amounts from 7-12 inches are possible in far north and west suburbs ahead of the arrival of powerful winds expected to gust above 40 mph Wednesday and Wednesday night.
The incoming system spanned sections of 25 states late Monday, extending from California to Pennsylvania and prompting advisories for all manner of meteorological trouble---from high winds to heavy snow and flooding rains. The storm swamped parts of the San Diego area with as much as 7.09 inches of rain at the same time producing 78 mph gusts in the San Joaquin Valley near Rosamond. The California mountains east of Sacramento were hit by 45 inches of new snow.
The system, which wends it way from New Mexico into Oklahoma Tuesday then north to Chicago by daybreak Wednesday, is predicted to undergo intensification, a process likely to strengthen winds dramatically.
Wintry storm's barometric pressures in league with the windy 1975 Edmund Fitzgerald storm
Howling winds are predicted to develop with the deepening storm Wednesday threatening blizzard conditions from Iowa to Minnesota, Wisconsin and northwest Illinois. Predictions of the storm's strength are on track to rival central barometric pressures recorded within the infamous November 10, 1975 Midwest storm responsible in part for sinking the Edmund Fitzgerald which sank on Lake Superior. Winds develop in such systems as air rises---often into a pocket of powerful jet stream winds which draw air aloft. The current storm's central pressure is predicted to drops to 28.93 inches (980 mb)- equaling the 1975 storm's lowest barometer reading, and a pressure which is not far from Chicago's all time lowest pressure of 28.70 inches set March 12, 1923.
Dear Tom,
I lived in Des Moines and remember December 2000 as being a brutal month with an excess of snow and cold. Was it as bad in Chicago?
Douglas Hanbury
Dear Douglas,
You bet it was. December 2000 in Chicago was incredibly cold and snowy. Much of the area received more than 40 inches of snow making it one of city's all-time snowiest months. The snow parade was highlighted by a major storm on Dec. 11 that brought 14.5 inches of snow to Midway Airport and 9.5 inches to O'Hare International Airport. In addition to the frequent and heavy snows, it was exceptionally cold. There were 10 days when the mercury dropped below zero including a string of six days from Dec. 20 through Christmas. The month averaged 10.6 degrees below normal and was the city's second coldest December on record, runner-up only to December 1983.
The first major storm of the winter will sweep into the Chicago area Tuesday night, bringing snow and rain followed by a blast of arctic air. Winter storm watches have already been posted for areas north and west of the city where the latest forecast tracks place the heaviest snowfall, which could total in the 6-12 inch range. Current forecast trends spare the city and areas close to 42-degree Lake Michigan a major snow with precipitation there expected to trend to rain for a while Tuesday night and Wednesday morning. These forecasts are preliminary, and a slight shift in the storm track could alter these predictions , so this storm's potential is still a work in progress.
Very cold air will sweep into the area in the storm's wake, powered by strong west-northwest winds that could gust in excess of 40 mph. The mercury is expected to drop into the single digits here for the first time since late February, and subzero lows could occur in areas with heavier snow cover on Friday morning. Heavy lake-effect snow will also fall in the snow belts of Lower Michigan and northwest Indiana.
Dear Tom,
What was the weather in Chicago like on Dec. 7, 1941?
Tom Zale, Tinley Park
Dear Tom,
It was typical early December weather on Sunday Dec. 7, 1941, when news of the surprise Japanese attack on Pearl Harbor reached the Chicago area shortly after noon. Skies were overcast and temperatures were holding in the middle 30s with gusty south winds making it feel even colder. Temperatures had climbed from an early morning low in the middle 20s on the way to an afternoon high of 38 degrees. The weather was dry, though a few snow flurries would fall across the city later that evening. Temperatures remained chilly in the following week, but spiked to near 60 in a pre-Christmas warm-up. Snow was not much of a factor that month, totaling just 1.7 inches with nearly an inch falling just before the New Year.
The mild days of November have become mere memories as wintry weather has quickly taken control in the Chicago area. Highs struggled to the freezing mark Saturday in the wake of Friday's subfreezing high of 28 degrees and the season's first measurable snow of 0.2 inches at O'Hare International Airport. Sunday's brief warm-up will be but a tease as three snow-producing systems take aim at the city in the upcoming week.
The first system of modest intensity will arrive by Monday morning bringing an inch or two of snow mainly to areas north of the city, but the second storm following close on its heels has the potential to bring a major-league dose of snow and cold to the area. The fast-moving storm should intensify as the sweeps across the Midwest Tuesday night and Wednesday and could bring blizzard conditions to many areas. Temperatures will plunge in the storm's wake, falling to single digits here by Thursday morning. A third storm arrives Friday with the potential for yet another round of accumulating snow.
Dear Tom,
There was a record warm spell in August 1953, and I recently read on this weather page that record highs were set in the fall. What was going on in 1953?
--Beth Swanick
Dear Beth,
For unexplained reasons, 1953 was a remarkable year in terms of unseasonable or unusually warm weather. The year hosted an unprecedented 22 new record highs, 16 of which remain in effect. The year's first record was set on May 30 with a high of 93 degrees and the final one established on Nov. 18 with a balmy 72. Most notable was a six-day stretch of record highs from Aug. 29 to Sept. 3 featuring back-to-back 101 degree days on Sept. 1 and 2. That was followed by a four-day string of record highs in the middle 80s from Oct. 19 to 22. A November warm spell produced five straight 70s, but only the 72 on Nov. 18 remains a record.
Measurable snow is finally on the books in Chicago. It arrived in Friday's pre-dawn hours three weeks beyond Nov. 16 -- the average date of the city's first measurable snow over the past 125 years. The 0.2" at O'Hare was the greatest to occur there in the 8 months since 2.1" on April 5. Residents of Chicago's northwest suburbs saw the area's greatest accumulation of snow with some 1-2" tallies reported near Crystal Lake. Flurries were interspersed with a good deal of sunshine Friday but produced no additional accumulation.
Southwest Lower Michigan wasn't as lucky. The late week arctic outbreak kept a steady supply of cold air streaming across Lake Michigan's comparably mild 44-degree waters Friday. Waves of lake snow resulted totaling 15" at Marne, 14" at Coopersville, 12.7" at Grand Rapids and 11.7" at Cannonsburg -- all in Michigan.
But while snow is no stranger to the Michigan lake snow belt in early December, the snows which fell farther south near the Texas Gulf Coast Friday were extremely rare. Snow accumulations up to 4" occurred 60 to 70 miles southwest of Houston at Lane City and Boling while an inch fell in the city itself -- the earliest measurable snow there since records began in the 1880s. The storm responsible is lifting from the Gulf into the west Atlantic and is to travel up the Eastern Seaboard Saturday and Saturday night and expected to produce significant snows and chilly coastal rains in a region which recorded record mild temperatures in the 60s only two days ago.
Area shivers in coldest air in the 9 months since March
Friday's high only managed to make it to 28-degrees at O'Hare -- the chilliest at the site since a 26-degree high on March 12. Temperatures late Friday evening had already fallen to 17 degrees at Rockford, Mundelein and Mc Henry to the northwest of the city and were expected to dip as low 12 degrees by Saturday morning in the coldest inland locations. Strengthening southwest winds should keep readings Saturday night from going that low -- and Sunday's highs should rise to within striking distance of 40.
Three snow systems -- one potentially a winter storm -- threaten next week
The Chicago area may catch up on its lagging seasonal snowfall quickly in the coming week if computer estimates are any indication. Only one in 7 years has produced a 6"-plus snow in Chicago the first half of December -- but there are signs this could be one of them. Snow may fall with three systems next week -- the first capable of generating a fairly modest accumulation Monday. A powerhouse 190 mph jet stream, expected to form as bitterly cold subzero air dives into the Plains and northern Rockies midweek, threatens significant storm development late Tuesday into Wednesday. This could send wind and snow into Chicago -- and potentially healthy snowfalls here or close by. A third snow is possible Friday.
A series of 44 computer snowfall projections produced by a range of forecast models over the past four days suggests total snowfall next week may average more than 7". 64% of the forecasts put snowfall here at a half foot or more, and the heaviest projections suggested as much as 12 to 14" might occur.
Dear Tom,
What is Chicago's biggest temperature drop in the shortest time span?
Kathy Roupas
Dear Kathy,
Having chilly Lake Michigan on our eastern doorstep makes Chicago a prime candidate for rapid temperature declines. Just before 2 p.m. on May 9, 1963, a fast-moving cold front sweeping south down the length of the lake dropped the lakefront temperature 22 degrees from a warm 84 to a chilly 62 degrees in just a minute and a half. On a longer time frame, a huge temperature drop occurred on Nov. 11, 1911, when the temperature plunged 61 degrees in just 8 hours from an unseasonably warm 74 degrees at 4 p.m. to a wintry 13 degrees at midnight. The largest 24-hour temperature drop in the U.S. took place on Jan. 23-24, 1916, at Browning, Mont., when the mercury plunged an incredible 100 degrees from 44 to minus 56.
The breadth of the cold air which has swept into the Lower 48 in recent days is stunning, sparing few areas of the country at least some impact. In Chicago, the chilly outbreak sets the stage Friday for the city's coldest temperatures in nearly 9 months. Friday's predicted 32 degrees is the coldest since the 26 degree high on March 12. For only the third time this season Thursday, flurries were in the air across Chicago---though only traces occurred. Farther north, snowfall, which erupted as cold air spilled into Wisconsin, totaled 3.9 inches northeast of Whitewater at Palmyra, 3.8 inches just southwest of Madison and 3.5 inches in the city itself as well as nearby Sullivan---nearly 2 inches of it coming down in under two hours. Other totals Thursday included 3 inches at North Prairie and 2.4 at Mt. Horeb. Flurries in Rockford late in the day produced slick spots which contributed to an accident on the Harlem Road Toll Bridge there.
Some snow flurries will continue across Chicago at times Friday into Friday night as the chilliest air in nearly 9 months tightens its grip. Only a trace of snow is on the books here since the beginning of the new cold season. By comparison, 4.3 inches had fallen by this time a year ago. It's a situation which is looking less and less sustainable as a growing number of computer models suggest significant snow may fall next week in two systems. The first, if current computer forecast scenarios hold up, is to bring a period of snow capable of producing modest accumulations late Sunday night into a portion of Monday. The second appears a more significant threat in terms of accumulating snow. Its projected path mirrors those which have ended up delivering some of the Chicago area's most potent snows.
That snowier days appear to lie ahead isn't a big surprise. Only 12 other years have had as little snow on the books at this late date as the trace which has been measured this year.
Gulf Coast from Houston to New Orleans on alert for wintry cocktail of precipitation
Snow is predicted in the Deep South and in some not so usual locations. Areas El Paso in far west Texas east to the Gulf Coast from Houston east to New Orleans are under advisories for snow or a wintry cocktail of rain, sleet and snow likely to end as snow.
Dear Tom,
Several years ago you had a WGN radio conversation with the late Bob Collins in which you spoke about "deep winter". Is there a time frame for that?
Dr. Douglas Squiers Kalamazoo, Michigan
Dear Dr. Squiers,
That was a long time ago but I was referring to a loosely-defined period of time from mid January to early February. Often referred to as "the dead of winter", these dates historically bring Chicago its heaviest snows and lowest temperatures. Some of the city's most extreme winter events have occurred during this time span, including the 23 inch "Big Snow" of Jan. 26-27, 1967, the Jan. 12-14 "Blizzard of '79" that was followed by the 29 inch record deep snow cover, and the all-time record low of minus 27 degrees on Jan. 20, 1985. Chicago has logged more subzero weather in February's opening four days than in any other time of the winter.
Not since last March has air this cold gripped the Chicago area. The chill is isn't abnormal by early December standards and certainly isn't barbaric. But it comes on the heels of this area's longest spell of above-normal November temperatures in the 107 years since 1902. Thursday's steady west winds and resulting mid 20-degree wind chills promise a decidedly more wintry feel to the air in the wake of an unprecedented 29th consecutive-day string of above normal temperatures.
Nearly three quarters of the Lower 48 extending south to the Gulf Coast---an extraordinarily large stretch of real estate---is involved in the early season arctic air invasion. The jarring weather realignment generated an intensifying storm Wednesday which drenched downstate areas of Illinois and Indiana. By late evening, Indianapolis had recorded 2.98 inches of rain while Mt. Carmel, Illinois had logged 1.13 inches and 1.00 inch was down at Carbondale.
Strengthening northerly wind gusts had reached 39 mph by late Wednesday evening at Whitney Young High School's WeatherBug station and 38 mph at Sauk Village. Cold air rapping into the intensifying storm, on a northeasterly track from Kentucky toward Canada's St. Lawrence Valley, was behind the powerful winds. At the same time, temperatures across the Chicago area were in a downward spiral, having dropped from 45-degrees at O'Hare around lunch time to the low 30s in the western suburbs late evening---a change which was prompting rain to mix with ice pellets and snow.
Storm drenches sections of Florida with 7+ inch rains
Heavy as rains were in sections of the Midwest Wednesday, the Southeast was drenched by storm's heaviest downpours. Tornado watches were out there much of the afternoon and evening there and a twister was reported to have touched down near Crestview in the Florida Panhandle near Alabama. Rainfalls were stunning---among them 7.05 inches at Sumatra, 6.84 at Wilma, 5.99 at Tallahassee and 4.73 at Apalachicola--all in Florida. Ft. Rucker in Alabama recorded 3.95 inches while Quitman, Georgia measured 3.60 inches.
Extraordinarily high barometric pressures predicted in northwest Canada this weekend suggest cold spell here not the last
Supercomputer forecast models are predicting eye-catchingly high barometric pressures across northwest Canada this weekend. Depending on the model examined, readings there are predicted to peak Saturday anywhere from 31.01 inches (1050 mb.) to as high as 31.60 inches (1070 mb)---levels much higher than any ever observed in Chicago. It's a signal the cold air buildup there is significant---a point driven home in the past week by several key cold weather indexes used by long range weather forecasters which are predicted to drop to the lowest levels of the season in the next 1-2 weeks. Experience has shown that pressures of that magnitude in that region of North America suggest additional cold air surges are likely to head for the Lower 48 in coming weeks. And 2 week computer snowfall estimates for Chicago continue to suggest the area could see spells of sticking snow during the period.
Dear Tom,
My father told me that he had heard that there is always some snow in Chicago before Thanksgiving. For the last 40 years it seemed right. Was this year an exception?
David Levine
Dear David,
While snow has certainly been lacking so far this fall, there was a trace of snow at Midway Airport on Oct. 24 and again on Thanksgiving morning. At the city's official O'Hare site, the season's only snowflakes fell early Thanksgiving morning, though some ice pellets were observed on Oct. 16. Since 1969 your dad's rule is pretty much true with two exceptions. In 1994 the season's first flakes didn't occur until Nov. 27--three days after Thanksgiving, and in 1999 the city recorded its latest first flakes on record on Dec. 5, 10 days after the Nov. 25 holiday.
November's extended spell of abnormal warmth spilled over into the new
month Tuesday producing the Chicago area's mildest December open of the
past 11 years. O'Hare's 55-degree high--a reading 15-degrees above
normal---has only been equaled or surpassed on Dec. 1 on only 12 of the
last 139 years. But the remarkably stubborn run of above normal
temperatures which has dominated Chicago's weather for nearly a month
is set to break dramatically with the onset of strengthening northerly
winds Wednesday afternoon. The winds are occurring on the back side of
an intensifying storm lifting northward from the Gulf of Mexico. The
system, which unleashed 2-3 inch downpours on east Texas and Louisiana
Tuesday and has prompted flood advisories across 7 southeastern states
Wednesday, is to intensify rapidly as jet streams above it combine
(phase.) Phasing jet streams provide an extraordinarily supportive
environment in which storms may intensity. That's because the marriage
of the cold air-transporting arctic jet stream with a more tropical
southern jet increases atmospheric "lift" encouraging moist air to rise
and cool as winds rush in from all sides with increasing speed. This
process leads to clouds and precipitation.
The latest storm's impact on the Midwest Wednesday will be to set the
stage for strengthening northerly winds expected to overpower the mild
temperatures with which Wednesday opens in Chicago. A thickening cloud
deck is eventually to hide whatever morning sun is able to filter
through the extensive high and mid-level cloudiness which has arrived
well in advance of the northbound storm. The rapid influx of moist air
predicted Wednesday afternoon will allow clouds to lower and threaten
chilly rain possibly mixed with some ice pellets or snow toward evening.
The storm's track continues to be monitored since any westward jog in
the Louisiana to Ohio path the system is currently predicted to follow
could increase precipitation coverage and intensity Wednesday night
beyond levels currently predicted. As it stands now, precipitation is
expected to switch to a period of snow from Chicago east for a time
Wednesday night and there could be enough snow to stick to colder
grassy surfaces at some location.
Lack of measurable snow by now rare; only 14 percent of past 125 years similarly snowless
The absence of measurable snow to date is rare. Only 17 of the past
125 years have failed to produce at least 0.1 inches by Dec. 2. But
snow enthusiasts shouldn't despair. While amounts predicted by
computer models the next several weeks vary widely, each of the most
recent 11 forecast cycles of the National Weather Service's Global
Forecast System (GFS) model produce measurable snow in the 1-2 week
range. The tallies average 7 inches---with individual forecasts
varying from 2.2 to as much as 16 inches. Observational records here
indicate an average of 3.5 inches of snow falls through mid-December
and that measurable snow has fallen in 82 percentof years at some point
in the coming two weeks.
Dear Tom,
I remember getting sent home from high school during a big snowstorm about 10 years ago. Can you pin-point this storm?
Barry Waldron
Dear Barry,
The storm was most likely the major snow that struck the Chicago area on Dec. 11, 2000. Though it had been snowing all night, conditions were not too bad for the morning commute and many schools remained open. However, the snow intensified through the morning, falling at the rate of an inch an hour and blown about by strong northeast winds that piled it into huge drifts. As conditions worsened, many schools and businesses closed early creating traffic gridlock. When the storm finally subsided, Midway Airport had recorded 14.5 inches of snow while O'Hare tallied 9.5 inches. December 2000 went on to produce tremendous snowfall, with Midway eventually logging 41.3 inches, a December record.
![snowfall_map(1) [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/snowfall_map%281%29%20%5B640x480%5D.jpg)
![December 26 - 5 - Copy [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/December%2026%20-%205%20-%20Copy%20%5B640x480%5D.jpg)
![December 26 - 8 - Copy [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/December%2026%20-%208%20-%20Copy%20%5B640x480%5D.jpg)
![December 26 - 1 (1) - Copy [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/December%2026%20-%201%20%281%29%20-%20Copy%20%5B640x480%5D.jpg)
![wgn pic's 003 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/wgn%20pic%27s%20003%20%5B640x480%5D.jpg)
![wgn pic's 004 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/wgn%20pic%27s%20004%20%5B640x480%5D.jpg)
![wgn pic's 006 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/wgn%20pic%27s%20006%20%5B640x480%5D.jpg)
![IMG_4827 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_4827%20%5B640x480%5D.jpg)
![IMG_4825 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_4825%20%5B640x480%5D.jpg)
![12 in snow [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/12%20in%20snow%20%5B640x480%5D.JPG)
![Cardinal Bird [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Cardinal%20Bird%20%5B640x480%5D.JPG)
![48thandRobinsonSnow-500 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/48thandRobinsonSnow-500%20%5B640x480%5D.jpg)
![Antioch [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Antioch%20%5B640x480%5D.jpg)
![DSC01309 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSC01309%20%5B640x480%5D.JPG)
![DSC01310 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSC01310%20%5B640x480%5D.JPG)
![holidayhouse [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/holidayhouse%20%5B640x480%5D.jpg)
![DSC01298 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSC01298%20%5B640x480%5D.JPG)
![DSC01305 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSC01305%20%5B640x480%5D.JPG)
![LakeSuperior1 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/LakeSuperior1%20%5B640x480%5D.JPG)
![Ryan S [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Ryan%20S%20%5B640x480%5D.jpg)
![Connie K [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Connie%20K%20%5B640x480%5D.jpg)
![DSCF5445 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/severe-weather/DSCF5445%20%5B640x480%5D.jpg)
![IMG_6139 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_6139%20%5B640x480%5D.JPG)
![Ice [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Ice%20%5B640x480%5D.JPG)
![Szepanski 1 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Szepanski%201%20%5B640x480%5D.jpg)
![Szepanski [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Szepanski%20%5B640x480%5D.jpg)
![piechota [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/piechota%20%5B640x480%5D.JPG)
![Bundy1 [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Bundy1%20%5B640x480%5D.jpg)
![Mcgrath 1 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Mcgrath%201%20%5B640x480%5D.JPG)
![McGrasth [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/McGrasth%20%5B640x480%5D.JPG)
![Elliott [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/Elliott%20%5B640x480%5D.jpg)
![miller [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/miller%20%5B640x480%5D.JPG)
![DSCF5422 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCF5422%20%5B640x480%5D.JPG)
![DSCF5423 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCF5423%20%5B640x480%5D.JPG)
![photo (1) - Copy [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/photo%20%281%29%20-%20Copy%20%5B640x480%5D.jpg)
![IMG_0910 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_0910%20%5B640x480%5D.JPG)
![IMG_0911 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_0911%20%5B640x480%5D.JPG)
![s 134n [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/s%20134n%20%5B640x480%5D.jpg)
![s 144n [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/s%20144n%20%5B640x480%5D.jpg)
![s 151n [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/s%20151n%20%5B640x480%5D.jpg)
![IMG_7071 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_7071%20%5B640x480%5D.JPG)
![IMG_7072 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_7072%20%5B640x480%5D.JPG)
![IMG_7085 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_7085%20%5B640x480%5D.JPG)
![IMG_7097 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_7097%20%5B640x480%5D.JPG)
![IMG_7103 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/IMG_7103%20%5B640x480%5D.JPG)
![DSCN8874 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCN8874%20%5B640x480%5D.JPG)
![DSCN9006 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCN9006%20%5B640x480%5D.JPG)
![DSCN8907 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCN8907%20%5B640x480%5D.JPG)
![DSCN8915 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCN8915%20%5B640x480%5D.JPG)
![DSCN8945 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCN8945%20%5B640x480%5D.JPG)
![1208091402a [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/1208091402a%20%5B640x480%5D.jpg)
![levin [640x480].jpg](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/levin%20%5B640x480%5D.jpg)
![depew [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/depew%20%5B640x480%5D.JPG)
![pearson [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/pearson%20%5B640x480%5D.JPG)
![DSCN4579 [640x480].JPG](http://weblogs.wgntv.com/chicago-weather/tom-skilling-blog/DSCN4579%20%5B640x480%5D.JPG)
-thumb-650x487.jpg)
