When damp and mild air rolls across Chicagoland at this time of the year, it is usually attended by extensive cloudiness, fog and rain. It’s the price we pay when winter temperatures climb 10-15 degrees above normal.
History tells us that Chicago’s readings climb into the 40s on only about one day in four during the first week of January, and so Sunday’s and Monday’s highs in the low and mid 40s constitute an early-January bargain. But it won’t last.
Cold air returns in earnest later this week, and temperatures plunge 30 degrees to levels that will run as far below normal by Saturday as they are above normal today.
Elsewhere, the weather is causing life-threatening troubles ranging from flooding rains (and massive mountain snows) across California, Oregon and Nevada to warm, desiccating winds across Texas and Oklahoma that have set the stage for grassland fire emergencies.
December 2005 Archives
Chicago’s ongoing mild spell was interrupted Friday afternoon as rain changed to snow for a few hours. By 8:00 p.m., O’Hare Airport had measured 0.2 inches, and Midway 0.3 inches. These meager sums did not stick as temperatures held above freezing.
Farther north, nearly a foot was expected in Minnesota and Wisconsin around Lake Superior. The storm causing the weather passed just north of Chicago. In its wake, Saturday’s temperatures will plunge across Chicagoland but remain above normal—especially the overnight lows.
Mild weather returns Sunday to greet the new year, but the fast-track of frontal passage every two days continues, with rain returning by Sunday night into Monday, and again Tuesday night into Wednesday. Thereafter, the jet stream buckles and divides the country in two. In the West, the series of pounding Pacific storms ends, while more normal winter temperatures return east of the Rockies.
The next in this series of fast-moving weather systems of Pacific origin arrives Friday afternoon with temperatures in the upper 30s and a good chance of rain.
Unlike its predecessors which developed after they passed east of Chicago, this system gains strength as it exits Iowa and tracks across northern Illinois. Updated computer models suggest upper-level dynamics will be strong enough to generate colder air in the lower 5,000 feet of the atmosphere—enough to change rain into snow here Friday night despite above-freezing temperatures at the surface.
As a result, wet snow may accumulate an inch of two on grassy or colder surfaces. The best of the snow crosses central Wisconsin with 6 inches of snow possible.
Thereafter, rain is likely with future frontal passages. By next Thursday, the mild pattern will begin to break down, and temperatures will plummet back toward normal.
During the first three weeks of December, the temperature averaged a frigid 11 degrees below normal, including one night below zero. Then the weather pattern switched: In the past week, temperatures have averaged 13 degrees above normal, during which time the low temperature has not fallen below freezing. Over the United States, the upper flow has been predominantly west-to-east with a powerful jet stream driving huge moisture-laden storms into the West Coast. Any remaining moisture and energy with these winter storms is dissipated over the Rockies, resulting in rather tame systems here with little rain or temperature contrast with frontal passage, now on a fast two- to three-day cycle.
Halfway around the globe, an upper low has settled over Europe, resulting in a steady diet of storm systems originating just east of Greenland. Wednesday’s storm brought central Europe to a standstill with significant snow, arctic cold and strong winds.
Abundant sunshine over Chicago in a mild pattern dating to last week teamed up to produce the highest temperatures of the month. O’Hare Airport topped out at 47°, while Midway reached 46°—the warmest readings this December. Not far to the north, clouds and fog lingered all day; Rockford reached only 36°.
The strong zonal jet stream responsible for the respite from the cold continues past New Year’s Day and into next week. High temperatures remain above normal, but the real mild air is measured by the minimums, which should remain 10 to 15 degrees above the current 17° normal low.
Upcoming weather systems in this pattern deliver respectable precipitation dynamics in the upper atmosphere, but not much moisture or contrast on either side of each passing cold front. Most precipitation will fall as rain, though flurries are possible on Saturday—the coldest day in the next seven days.
The string of above freezing hours ended at 106 hours when the temperature at O’Hare dipped to 32° at 9:00 p.m. Monday. Nonetheless, the ongoing mild trend continues, with today’s high expected to reach into the mid 40s, nearly 15° above normal and perhaps the warmest of the month. The high for this month stands at 44° recorded on the Dec. 23.—on the cool side since 84% of all previous Decembers have reported at least one 50° reading.
The current spate of cloudy days lingers until at least the weekend as a stubborn layer of moisture remains trapped in the lower layers of the atmosphere. In addition to the gloomy cloudiness, weak systems of Pacific origin will traverse the country, touching off light rain from time to time, and even a snow shower to close out the year on Saturday.
In a dramatic about-face late last week, the persistent cold weather for the first three weeks of December have flipped to well above-normal readings, including 84-plus straight hours above freezing temperatures beginning last Thursday morning.
This mild spate should continue through the week, tapping air now in the central Plains. On Sunday, Denver reached a record high of 69° with westerly Chinook wind. A modified version of this mild air spreads east early in the week, with 45° possible at Chicago on Tuesday.
The catalyst for the change is the breakdown of the upper ridge in the West, which had forced frigid arctic air southward with a northwesterly jet stream. Now, the jet stream flows zonally west-to-east, bringing mild Pacific air with above-normal temperatures to most of the country. Respectable Pacific weather makers slam into the Northwest, but dry considerably before reaching Chicago.
The first three weeks of December, characterized by bone chilling cold and continuous snow cover, have yielded to a milder regime as the arctic air retreats north and east. As of midnight Sunday morning, Chicago (Midway) has reported 61 hrs. of continuous above freezing temperatures--since 11:00 a.m. Thursday morning. This air, mild by December standards, has teamed up with south winds, high dew points, and rain to steadily erode the snow cover to less than one inch late Saturday.
Little change in the current mild pattern is expected right through the end of the year, with a good chance that high temperatures will top out above freezing every day with little precipitation. As a result, Chicago should once again report little or now snow cover in the week between the holidays, a trend began in the early 90s.
The White Christmas which seemed assured just a few days ago is in jeopardy. Friday’s temperatures soared into the 40s across the region for the first time this month. Combined with higher dew points and south winds, the snow cover was cut in half. Midway’s 6 a.m. report of 5 inches was reduced to 2.7 inches by 6 p.m., while O’Hare melted its 3 inches to a scant 1 inch. Further melting is likely Saturday with rain and 40° highs.
Rain is unusual at this time of year, occurring only 10 percent of the days on Christmas Eves past. This rain mixes with snow overnight Saturday, and tapers off to flurries early Christmas morning before ending.
Thereafter, a zonal west-to-east jet stream will keep arctic air locked north in Canada, suggesting temperatures each day will climb above freezing. Any frontal passage during this time should be weak with little precipitation.
All of Chicagoland recorded the warmest readings since late November, with O’Hare climbing to 38°. For winter-weary Chicagoans, milder above freezing high temperatures should continue right on through the next week. Friday’s high should easily reach into the 40s for the first time this month. On only two occasions since 1870 has December failed to reach 40°, most recently in 2000, when the high for December was only 36° and the monthly snow totaled 41.3 inches. This December, Chicago is currently running 11.2° below normal with 10.1” of snow.
However, amidst this warming trend is a chance for a fresh coating of new snow in the morning hours of Christmas as a developing low passes to our south. With the absence of arctic air and high dew points, most precipitation should occur as rain before changing to snow near the end of the event Christmas morning.
Strong gusty southwest winds signal the end to one of the coldest starts to December ever. Chicago has experienced only three daytime highs above freezing so far this month (through December 21), eclipsing the previous record covering the 136 years since 1870 of just 4 above freezing days back in December 1-21,1919. High temperature forecasting has been challenging to say the least this week, with a persistent wind flow over hundreds of miles of snow cover to the west and a very dry cold high pressure air mass in place. Cold air at the surface was actually further entrenched by the stabilizing influence of warmer air aloft. Winds are to become more southerly the next 24 to 48 hours and increase in intensity, flowing over a broad expanse of thin or no snow cover to the south. The evaporative effects of the winds as well as warmer temperatures followed by an period of rain should result in a fast snow melt over NE Illinois.
Warming enters its third day Wednesday, but the process is occurring far too slowly for many area residents, weary of the relentless nature of this month’s chill. Arctic air has dominated, allowing only fleeting respites from the bitter chill. That’s evident from the fact 90% of the month’s daily temperatures have averaged below normal.
December has managed only three days above 32°—one-fifth of last year’s 15 to date and well below the 136 year average of 14 days by the 21st. The month’s mildest single temperature has been 35°, a far cry from the three 50° highs which had occurred by this point in December one year ago.
The month’s 18.2° average maintains December’s rank as Chicago’s 4th coldest, far from the 30.2° average since 1870.
Things are improving. Highs here reached 11° Monday, 21° Tuesday and should hit 31° Wednesday and 37° Thursday.
Chicagoans were greeted by frigid arctic air again Tuesday morning.
Coming days will see quite a temperature inversion develop as incoming
mild Pacific air floods into the area. Thus, the hint of haze captured
in this shot looking southeast at the Metra Tracks in Cary, Illinois and
taken by Anson Mount will become a more obvious feature in the days
ahead--especially as temperatures surge above freezing Thursday and
Friday and melt snow. Temperature inversions--a state of the atmosphere
in which warm air sits atop cold air reducing or eliminating the usual
decline in temperature with height, decreasing or overcoming the usual
vertical mixing of air which occurs when warm, buoyant air is near the
surface and ascends into colder, denser surroundings---often allow the
build-up of haze. As a result, much hazier environment is likely later
this week.
-- Tom Skilling
Photo courtesy of Anson Mount
There’s nothing unusual about cold winter weather in Chicago. But, the intensity of the chill we’ve endured in recent weeks is quite unusual for this early in a new cold season. The opening 19 days of the month have averaged 18.4° making it the fourth coldest December open since 1870. It’s a temperature 14.3° below a comparable period one year ago and only 1.3° away from than the coldest Dec. 1-19 period on the books in the city: 17.1° in 1958. Monday’s 11° high was the coldest December daytime temperature in 5 years. Only 46 December days have been as cold or colder since 1870.
The area’s first official sub-0° low of the season occurred at 8:30 a.m. Monday when O’Hare’s readings reached -1°. West suburban DeKalb and Rochelle hosted the area’s coldest lows of -7°.
Heating this air without adding moisture Monday produced indoor humidities of just 4-6%, a fraction the 35% considered comfortable by most.
-Tom Skilling
Melissa Pavlica of Westmont snapped these photos of "sun dogs" Monday
morning. Sun dogs result as incoming sunlight is refracted by ice
crystals, producing a halo, two segments of which are visible, giving
the appearance of a sun on either side of the disc of the sun. Monday's
extreme cold, including -1 at O'Hare, 0-degrees at Midway, -6 at west
suburban Aurora Airport, -1 at Waukegan and -5 at Rockford no doubt
contributed to the presence of the airborne ice crystals which created
this visual phenomenon.
- Tom Skilling
Photo Courtesy of Melissa Pavlica
Anchorage has had unusually mild weather lately but very little (like
none) sunshine. However, my friend and fellow meteorologist in Anchorage, Tom
MacPhail, reported FINALLY seeing the sun Monday albeit briefly. He
snapped this picture of a spectacular sunrise which occurred at 10AM.
During late December near winter solstice in Anchorage, the sun is only
above the horizon for a brief 5 hours per day and even then never gets
very high in the sky so provides little if any warmth. Tom reports
that..."Thankfully, we're nearing the end of the tunnel and days begin
getting longer after Dec 21; very gradually at first...a few seconds per
day...but accelerating to a gain of about 5 minutes per day by late
January." Anchorage's daylight begins to feel normal again by
mid-February and by late March, they are already getting over 12 hours
of sun above the horizon. By June's summer solstice, the sun is up over
19 hours per day and darkness comes in the form of a short period of
dusk between midnight and 4AM. It is truly a land of extremes!
-Tom Skilling
Photo courtesy: Tom MacPhail
The week ahead starts off with a cold, dry arctic air mass still holding fast over the western Great Lakes and Midwest. However, jet stream flow aloft will shift from north to west midweek, allowing maritime cool air from the West Coast to finally penetrate into the central Plains. The warm-up should begin Thursday and peak Friday with 40°-plus high temperatures forecast for the first time this month. There have been only two Decembers in 135 years of record that did not have at least one 40° day—1983 and the snowy December of 2000—and two others, 1903 and 1919, only had a single 40° day.
The Northeast Illinois snow cover ranges from around 3 inches south to 6 inches north along the Wisconsin-Illinois border. As winds pick up Wednesday, warm air moves in Thursday and rain spreads over the area later Friday into Saturday. The snow pack will slowly diminish with a good chance of bare spots by Christmas Day.
WGN-TV meteorologist Richard Koeneman sent these images of the Blue Ridge Mountains of western North Carolina, which experienced a 10-hour period of freezing rain Wednesday night into Thursday. The freezing rain left an ice accumulation of 3/8th inch on mountains and ridges above 4,000 feet.
Below are views in the mountains above Fairview, N.C., on Friday. Asheville lies in the valley beyond the ridge in the center of the lower photograph.
Northerly jet stream winds aloft will continue to steer arctic cold into the western Great Lakes and northeast Illinois, but Wednesday the pattern is expected to change with a more west to southwest flow gradually guiding cool maritime-source air from the west coast into this region. High temperatures should slowly nudge higher, reaching well into the 30s Thursday and 40s Friday as strong southwest winds take over at ground level accelerating snowmelt and the shrinking snow cover. Much of the week ahead low pressure systems will be concentrated along the Canadian border to the north and the Gulf of Mexico to the south, resulting in very little in the way of precipitation for northeast Illinois. Moisture will be on the increase Friday with rain likely Christmas Eve in advance of an approaching Central Plains low pressure system. The late-week warming combined with Saturday’s anticipated rain could eradicate much of the current snow cover by Christmas Day.
The breadth of December’s chill across the Lower 48 has been stunning, extending from the Pacific Northwest to New England and south to northern Florida. It’s an important reason why snow now covers 43 percent of the country—two and a half times the area a year ago. Another 1.1” was added to Midway’s tally in bursts of snow early Friday, boosting the 2005-06 seasonal total there to 17.3”—5.5 times the amount by this date last year. It’s the city’s sixth snowiest open since 1928.
Chicago’s not alone with snow. Many Midwest cities have measured five or more times the snow on the books by this time last season. Just east of Duluth on western Lake Superior, snow has fallen non-stop since Tuesday night.
While Chicago has shivered, mild and rainy weather has pushed Anchorage, Alaska’s, average December temperature nearly 4 degrees warmer than Chicago’s: 23.7° vs. 19.8°.
Thunder and lightning accompanied a quick burst of heavy snow at Kankakee late Thursday. Thundersnow was also reported in sections of Indiana and Ohio. Still other snow showers slashed visibilities to a quarter mile late Thursday evening in north suburban Algonquin. The squally snows erupted beneath a frigid pool of cold air aloft which eased across the area and lingers Friday. The huge vertical temperature declines which developed produced what meteorologists refer to as an explosively unstable environment—one in which air is encouraged to ascend and cool to saturation. The result is clusters of clouds with tops to 10,000 to 15,000 feet capable of producing bursts of snow. Tiny upper air impulses embedded within the jet stream aid the process.
Thursday’s 0.2” of snow marked the 9th day with measurable snow of the month. That’s more than the typical number in a full December and triple the three measurable snows which occurred a year ago.
--Tom Skilling
Thursday dawns foggy and drizzly in the midst of Chicago’s mildest daybreak temperatures in 17 days. Not since a 39° low on Nov. 28 has it been any milder here. The flood of mild, moist air into the area in combination with the natural settling of snow since last Thursday’s snowstorm has trimmed six inches from the area’s still-extensive snowpack at Midway Airport in just the past 5 days—from 11” last Friday to 5” by late Wednesday evening.
A burst of snow early Wednesday produced over an inch in surrounding areas, including 1.5” at Antioch, 1.1” at Arlington Heights and 1.8” at Lake Villa—north and northwest of the city—while 2.1” fell at Plainfield. Downstate Springfield reported 3.5” before a switch to rain occurred.
With Midway’s 0.2” of snow Wednesday, the seasonal tally reached 16”, the 7th snowiest early season tally since 1928.
-Tom Skilling
Snow has covered the ground on December 14 only 23 of the past 78 years at Midway Airport— less than a third of the time. It’s a revelation likely to surprise many Chicagoans who have come to assume December and a covering of snow go hand in hand. Observations of the snow cover at Midway Airport indicate the ground has been snow-free here on this date more than 70% of the time since 1928.
That’s not the case this year. In fact, the 7” on the ground before Wednesday’s incoming storm has been exceeded only once on this date since records began in the late 1920s at Midway. That occurred five years ago in 2000 when a 17” snowpack was in place.
Wednesday’s predicted snowfall, likely to be the second heaviest since November, is the 12th measurable accumulation of the new season.
Only two other years since 1884 have produced more days of measurable snow by now—1989 with 14 days and 1972 with 17 days.
Snow--this time wet and heavy---threatening season's second significant accumulation Wednesday and a rainy late day mix of precipitation over part of the Chicago area
Wednesday's storm is likely to produce snow quite different than last week's fluffy 10.2" accumulation at Midway Airport--and there's likely to be more wind with it (20+ mph gusts from the southeast appear a good bet). This snowfall is to take place as wet and heavy flakes--not the huge, LIGHT flakes which fell last Thursday in the city as lake moisture enhanced snowfall. Temperatures Wednesday, predicted to hover with a degree or two of freezing, promise more common 10 to 1 snow to water ratios rather than the light 26 to 1 ratio snow of last week---snow which fluffed up to more than twice the volume of conventional Chicago snows because of the cold environment within which it occurred. That's likely to make Wednesday's snow more difficult to shovel. Those planning to shovel would be wise to approach that task with added care.
Another potentially noteworthy twist to Wednesday's snow may be the ultimate transition to a mixture of rain and snow mid and late afternoon Wednesday from Chicago south. This will come after a number of hours of significant snowfall and potentially significant accumulations over much of the area. Such a change would occur after a significant accumulation expected to fall--perhaps in the 4-5" range (heavier north) from the city and north--with lighter amounts more in the 1 to 3" range south. (Note: North suburban locations are far less likely to see any widespread liquid precipitation during the heart of Wednesday snowfall, although mixed drizzle can't be completely ruled out late in the upcoming precipitation event.)
Sections of north-central and northwest Illinois as well as Wisconsin and Minnesota are to bear the brunt of this storm's accumulation with heavier totals than those observed in Chicago. While the predicted snowfall in Chicago appears on track to become the second major accumulation of a season which is already the snowiest since 2000 (December's seen almost 9 times the snow of the ENTIRE month of December last year--and the month's not even half over!!). Totals there may well exceed 6"---and may even approach 10" in locations near LaCrosse and Eau Claire, Wisconsin and in and near Rochester and the Twin Cities in Minnesota if current forecast trends continue. Closer to home, Chicago's south suburban areas may see a complete transition to rain during the mid and late afternoon and evening after a couple inches of slushy accumulation.
Advisories, watches and warning have been hoisted across sections of 9 central states--from the Dakotas east to Michigan and Illinois. The best indication now is that snow may overspread the Chicago area between 8 and 10 am Wednesday morning then continue steadily much of the afternoon. Precipitation may become more sporadic and far lighter as the strongest jet stream winds reach the area late in the day and Wednesday night. (Heaviest storm precipitation occurs on either side of the strongest channel of upper air winds--regions meteorologists refer to as "shear zones" because of changing wind velocities in such zones. Interestingly, those high altitude wind speed variations play an important role in setting up the vertical air motions (the so called "lift") which acts to cool air converting the incoming moisture into clouds and precipitation.
-- Tom Skilling
It’s been five years since Chicago’s early season snowfall tally has been any higher at the city’s Midway Airport observation site than the 15.8” currently on the books. That’s the year December went on to produce a record 41.3” of snow—the greatest amount ever for the month. The seasonal total through Dec. 12, 2000 was 18.2”.
Of this season’s 15.8” on the South Side, 14.6” has fallen this month. That’s 8.5 times all the snow which fell last year during the entire month of December (1.7”).
For two weeks, temperatures have averaged well below normal. December 2005’s average of 17.6° in the opening 12 days of the month is 20° below the same period a year ago. Five nights last Dec. 1-12 boasted temperatures warmer than any of the warmest daytime readings recorded to date this month.
-Tom Skilling
For the first time this December, temperatures in Chicago broke the freezing mark just after midnight Sunday morning as a burst of milder air reached the city following a light snowfall, sending the mercury to 33º. The thaw was brief, lasting for only two hours before the cold air returned and temperatures dropped back into the 20s.
The persistent cold spell, now entering its third week, shows little sign of retreat, and while only a few flurries are on tap in Chicago today, several inches of lake-effect snow can be expected in the northwest Indiana and southwest Michigan snow belts, where up to 6 inches of snow fell Sunday.
Forecasters are keeping an eye on a developing weather system that may bring this month’s second significant snow to Chicago on Wednesday and Thursday. Snowfall this season is already approaching 16 inches at Midway Airport, a value not reached there until Jan. 20 last winter.
A fast moving weather system brought up to a two inches of snow to the Chicago area late Saturday, just 48 hours after Thursday evening’s 6 to 10 inch ordeal. The week ahead promises more of the same as early season cold and snow continue to grip the city.
Early Sunday morning Chicago temperatures crept up to 33º preventing the city from breaking the 11 day record for consecutive days with temperatures of 32º or lower for so early in the season which was established from Nov. 28 to Dec. 8 in 1976. With Saturday's high of 32º reached just before midnight, the city was able to tie the existing record. This morning's 33º high reached at both 1 and 2 a.m. were the city's first thawing temperatures since since Nov. 29, when the mercury climbed to 39º.
Another round of light snow could bring small accumulations tonight, but computer models show a gathering of forces in the Midwest later this week that could produce the month’s second significant snowstorm.
It’s official—the abnormal chill which first roared into Chicago 11 days ago has produced the coldest Dec. 1-9 average temperature on record—16.7°. That’s a reading nearly 16 degrees below normal.
The area is on the verge of a second temperature record—this one for the greatest number of consecutive early season subfreezing temperatures. Saturday’s 27° predicted high becomes the 11th straight day of subfreezing temperatures, tying with 1976. A reinforcing burst of cold air Sunday is to produce a 12th subfreezing day—a new early season record.
The snowpack which blankets the Lower 48 continues to expand, according to a NOAA analysis. On Friday, 58.2 percent of the country was snow-covered compared to 9.6 percent a month ago and 22.1 percent the same time a year ago.
It’s one factor behind another day of record cold air Friday across four states from Texas to Missouri.
A snow accumulation as heavy as Thursday’s 9.3” at Midway Airport has occurred in December only once every 9 years. The snow, which fell at 1-2” an hour—as much as 3” in the hour between 5 and 6 p.m.—dropped visibilities under a quarter mile at times and created a nightmarish evening rush hour. Commute times from the Loop to northwest suburban Woodfield—normally about an hour—slowed to 5 hours. Road crews were forced to battle rush hour traffic as they plowed snow and dispensed road chemicals.
Thursday’s storm, by far the heaviest of the season, pushes the Midway Airport seasonal snow total to 13.3”—one of the five heaviest on record since 1928 and the heaviest since the infamous season of 1978-79, the snowiest on record here. That season went on to produce 89.3”. Perhaps ominously, a review of previous seasons with heavy early season snow tallies indicates most went on to huge full season surpluses—averaging 65.9” vs. the normal 42.9”.
-Tom Skilling
Preliminary Storm snow totals just before 7 p.m
Midway Airport 8.3"
North Side near Peterson & Western 5.5"
WGN Studios (Addison & Western) 4.5"
South Bend, IN 3.9"
O'Hare 3.2"
Arlington Heights 2.5"
Rockford 1.9"
Romeoville 4.8"
Oakbrook 5.2"
LaGrange 7.0"
National Weather Service has upgraded the Snow Advisory to a Heavy Snow
Warning in Cook County and counties adjoining the lake in northwest
Indiana. Snow falling heavily across the far northwest suburbs (sections
of northwest McHenry, Winneobago and Ogle counties) at 7pm.
MIDWAY STORM SNOWFALL SURGES TO 7.7" AT 6 P.M.
3" NEW SNOW PAST HOUR ALONE!
The South Side of the city and southern suburbs--east across northern
Indiana--are being hammered by lake-enhanced storm snowfall. Snowfall
as of 6 p.m. Thursday evening has reached 7.7" at Midway, three inches
of which has fallen in the past hour alone! That suggests we may be
headed for local 9-10" totals there before this system exits the area
later tonight. By contrast, Steve Kahn, veteran meteorologist and fellow
Tribune/WGN-TV Weather Office colleague, reports just 2" down at in our
northwest suburbs at Arlington Heights. O'Hare's tally is at 2.3"--and
the snow continues to fall. The snow/water ratio at Midway Airport is
running 29 to 1 (rather than the usual 10 to 1—indicating EXTREMELY
fluffy snow and supporting the notion Lake Michigan moisture is
enhancing the snowfall. Snows to the east in Indiana are strictly storm
related and are falling in the area of maximum lift being generated by
the sharp upper atmospheric trough which is helping drive this storm.
SEASON'S BIGGEST SNOW TO DATE HITS AT FRONT END
OF A STORMIER PATTERN WHICH COULD LAST INTO MID-DECEMBER
The season's biggest snowstorm is in progress and likely to last into
the night. Accumulations have reached 3.5" at Midway Airport (as of 5
pm) and exceed that amount in the southern suburbs where snow has
fallen longest (since 1-2 p.m.) Mundelein in the northwest suburbs has
reported just an inch. Snowfall reached the city proper 2-3 pm and is
currently accumulating at 1" an hour, slashing visibilities at times
to a quarter mile. Snow may fall until just after midnight with the
heaviest intensities likely through 10 or 11 p.m. Final accumulations
may range from 2-3" in the Wisconsin border area to 3-5 inches
(locally as much as 6" in spots) in the city proper and closein
suburbs and up to 6-8" in Chicago's southern suburbs, including much
of Indiana. It's the 8th measurable snow of the new cold season and
easily the biggest. It's also a VERY fluffy snow. Measurements by
Frank Wachowski, veteran Midway Airport observer and Chicago
climatologist, indicate this evening snow is a 23 to 1 snow to water
ratio snow versus the more typical 10 to 1 ratio often cited as
"normal".
The evening commute is being described as nightmarish--with
commute times from Chicago's Loop to Schaumburg estimated at over 4
hours. Normally it's less than an hour.
A typical December produces 6-7 instances of measurable snow
here. Of the more than 550 measurable December snows logged at Midway
Airport since 1928, 95% have produced accumulations under 6". And the
snow's not limited to the Chicago area. 20 states from Illinois and
Indiana to much of the Mid-Atlantic and Northeast--including all of
the major East Coast cities from Washington to Philadelphia, New York
and Bosto----are under one form of winter weather advisory or another.
This storm appears, from latest computer projections, to mark
the beginning of a stormier than normal pattern, which could last over
much of the U.S. for at least the the next few weeks. This raises the
possibility several other significant winter storms may be the
country's future during that period. While the coldest temperatures
are pulling back a bit in the Midwest, nothing close to resembling a
real or prolonged thaw is in the cards and December, already among the
coldest on record. The month is likely to remain cold. There are even
signs the cold air in the arctic will recharge in coming weeks,
potentially forcing another round of bitterly cold air into the
nation's heartland and impacting a larger area of the country, in the
1-2 week time range.
Tom Skilling
It’s been 63 years since December has opened any colder.. The first 7 days of the month have averaged a bonechilling 16.8°—far short of the 33° long-term average the past 136 years and a stunning 20° below a year ago. Year to year temperature variations are seldomly larger. The chill predicted through week’s end is all but certain by Friday to make the month’s first nine days the coldest on record.
The unusual nature of the current cold spell shows up in other stats as well. Wednesday’s 0° morning lows at Midway and O’Hare join only eight other years since 1895 in which 0° temperatures have arrived AS early or earlier. Aurora’s -10° was the Chicago area’s coldest. Rockford bottomed out at -8°. Romeoville and Waukegan started the day at -5°.
Wednesday’s 15° high was the third straight day of teens—something which occurs on average in early December only once every 45 years.
--Tom Skilling
Midwesterners are accustomed to cold winter weather. But, this December’s opening week ranks among the coldest on the books in more than a century. Chicago’s 18.3° Dec. 1-6 average is more than 15° below the long term average temperature and has moved from 9th to 6th coldest on record since 1871.
Area residents away from the city and lake side locations must deal with sub-zero temperatures early Wednesday, readings not typical here for another three weeks. It’s the most intense chill here in at least a year—and, at colder locations, in nearly two years—since the -6° low on Jan. 31, 2004.
Chicago’s 17° high Tuesday missed the record for coldest daytime maximum (16° in 1893) by only 1°. Residents of Wisconsin weren’t as fortunate. The highs at Madison (11°), Wausau (5°), Marshfield (5°) and Oshkosh (11°) tied or broke the record for coldest max temperature Tuesday.
Lows dropped to 0° overnight in much of Chicago's far west suburban area—and sub-zero lows may be more extensive away from Lake Michigan and the heart of the city Tuesday night. This shot, taken at frigid Waukegan Airport looking southeast toward the Waukegan power plant around 7 a.m. Monday by pilot Anson Mount, drives the point home.
--Tom Skilling
Photo courtesy of Anson Mount
Temperatures have plumetted to January levels in the past week. The opening five days of December have averaged nearly 20° below normal and rank ninth coldest of all such periods on record in the past 135 years. The chill has forced area residents to increase home heating 80%.
Tuesday marks the seventh consecutive day to remain below freezing and easily the coldest yet. With a high of just 12° predicted at O’Hare, the record for coldest daytime high on Dec. 6 (16° in 1893) is in jeopardy. Only two days all of last winter were as cold.
Nighttime readings will drop below zero over much of the metro area Tuesday night. A chill of that intensity usually doesn’t arrive here until the final days of December or early January.
The cold air broke records in Chicago Monday morning with lows of 4° at O’Hare and 6° at Midway. Records occurred in at least 20 other locations across 4 states.
With the polar jet stream far south of the Ohio River in a mid-winter position, cold Canadian-source high pressure air masses have dominated the Great Lakes and Midwest weather pattern the first few days of December. With the fresh snow cover enhancing the effects of the cold air mass, the work week ahead for Chicagoans portends temperatures nearly 14 degrees below normal. Computer models indicate the polar jet may briefly buckle back north next weekend, but then quickly re-establish back to its present position with a fresh infusion of northwest flow aloft and colder air resuming the following week of Dec. 11-17. At least until mid-month, the primary storm track will be from Texas east through the Southeast U.S. with periodic severe thunderstorm outbreaks and heavy rains over that area.
In the eastern Atlantic, Epsilon—the 26th named storm of the 2005 season—was forecast to drift southwest and eventually weaken to a tropical depression.
Low pressure moves away to the east, leaving in it’s wake a 1 to 2 inch snow cover over much of the metro area. North along the Illinois-Wisconsin border snow depths may be closer to three to 5 inches. This snow cover will act in concert with cold Canadian high pressure air masses during the week ahead to give Chicagoans one of the coldest starts to meteorological winter on record. High temperatures for the work week are forecast to average 15° below normal.
Yesterday’s high of 30° may hold as this December’s warmest reading until next Saturday. If that is the case, it will be the first time in 135 years of record that Chicago high temperatures failed to warm above 30° the first 9 days of the month.
While highs struggle to warm into the 20s here, the country’s primary storm track will be south of the jet stream through states adjoining the Gulf of Mexico and the Southeast coast where severe thunderstorms are expected today.
December’s off to a very wintry start and likely to stay that way through the coming week. High temperatures the past three days have averaged 26.6°—a reading more than 13 degrees below normal. It’s been colder here this early in the season in only three previous years since 1930, including 1976, 1964 and 1942. With accumulating snow on the way expected to cover the ground, even colder readings lie ahead. The relationship between snow and cold weather is symbiotic. Snow reflects sunlight back to space before it can warm the atmosphere. And, at night, cooling occurs with special efficiency when a snowpack is in place. It’s a major reason lows dropped to a record-breaking -15° Friday at Huron and -13° at Sioux Falls—both in South Dakota—and why the season’s first single digits at O’Hare are likely Sunday night.
Highs stay in the teens or 20s the next 7 days. There’s never been a Dec. 1-9 period here which has failed to host at least one 30°.
Winter 2005-06 is off to quite a start this year in our 49th state according to friend and colleague Tom MacPhail, veteran Alaska meteorologist and aviation forecaster at the National Weather Service's Anchorage Forecast Office. Tom has sent us these images of a phenomenon known as HOAR FROST taken in Anchorage. Hoar frost forms during with some frequency during periods of ICE FOG—fog which occurs in bitterly cold environments with temperatures well below freezing (if not 0 degrees). Supercooled water droplets in the fog coat trees, vegetation and other outdoor objects in a shimmering covering of ice crystals.
Tom offers us some thoughts on Alaska's cold season-open this year:
"For the first time in the past few years, southern Alaska is having a truly cold start to their winter; more like the kind of winters enjoyed in the early 80s. It has been consistently below freezing since mid-October with the exception of one brief warm-up ahead of a storm in the middle of November."
Photos courtesy of Tom MacPhail
Chicago enters a third consecutive day of sub-freezing temperatures Friday and may not emerge from the Deep Freeze for at least the next 7 days.The last time Chicagoans experienced an above freezing temperature was 6 a.m. Tuesday morning. If the sub-freezing chill actually manages to hang on over the coming week, it would mark only the second time in 136 years of official observations here that the first week of December has failed to produce a daytime high above 32°.
Friday’s predicted 24° high is likely to become the coldest daytime reading of the season. It’s the third straight day of 20s—something which typically doesn’t happen for another three weeks. Snow on the ground provides arctic air an easy path into the Midwest. It will be a major factor in allowing cold spells of increasing strength to take hold in coming days.
