Meteorological winter---the three month period from Dec. 1 through the end of February---gets underway Tuesday--- but you'd never know it from the day's weather. A year ago, 2.7 inches of snow fell here. But this year, temperatures are predicted to surge into the 50s---a level more typical of late October than early December and 13-degrees above normal. The mild temperatures come on the heels of a November which closed at midnight as the sunniest and mildest here in 8 years. The Chicago area enjoyed 52 percent of its possible November sun---40 percent is normal---and the month's 45.3-degree average temperature qualified as the 9th warmest November in 139 years of weather records. Monday's 41 and 30-degree extremes made it the 27th consecutive above normal day---the longest string of above-normal readings to occur in a November here in the 107 years since 1902!
True winter bursts on the scene mid and late week
Huge weather changes loom in the wake of a mid-week storm expected to lift from the Gulf of Mexico into the eastern Midwest by late Wednesday. An outbreak of frigid early season arctic air is to ensue Thursday and Friday bringing Chicago its coldest temperatures in the 8+ months since early March. Daytime highs may well rise no higher than the mid to upper 20s---the first below normal temperatures in nearly a month.
The storm system predicted to lift northeastward along the cold air's leading edge, threatens the Chicago area with cold rain Wednesday afternoon. Gusty north winds are to induce some evaporative cooling in the lower atmosphere allowing the cold rain to mix or change to ice pellets by Wednesday evening---and to ALL snow for a time Wednesday night. Just how much snow falls will be critically dependent on the track the storm ultimately follows. A consensus of computer generated storm tracks has the system lifting from Louisiana north/northeast into eastern Lower Michigan between Tuesday and Thursday mornings. A suite of 22 of the most recent precipitation estimates predicted by nine different computer models suggests Wednesday night and Thursday could see snowfall here ranging from 0.2 inches on the low end to as much as 5.7 inches on the high side. The average of ALL current computer snow estimates on the system comes in around 2.4 inches.
Snow Wednesday night and flurries Thursday into Friday are close to "on schedule"
Chicago's snow record shows that the average first date of 1 inch or more snow has slipped in the past 11 years from Dec. 1 to Dec. 11. 46 percent of the years since 1884 have seen a 3-inch or greater snow between Dec. 1 and Christmas (Dec. 25).
Dear Tom,
There have been just a few Atlantic hurricanes this year. Wasn't global warming supposed to cause more of these storms?
Robert Roeder Des Plaines
Dear Robert,
The anemic 2009 Atlantic hurricane season ended on Nov. 30, with just nine named storms including three hurricanes, making this the quietest season since 1997. For the first time in three years no hurricanes made U.S. landfall. While the premise that global warming will raise ocean temperatures resulting in more and stronger hurricanes has gained acceptance by some scientists, much of this year's lackluster season can be blamed on El Nino, which produced strong upper-level winds across the Caribbean and western tropical Atlantic. El Nino is expected to strengthen this winter and continue into spring, but it is far too early to say if the 2010 season will be impacted.
The last day of November will see Chicago's 27th record-setting consecutive day with above-normal temperatures. Warmer readings are likely Tuesday as southwesterly winds and abundant sunshine allow afternoon high temperatures to approach and even exceed 50 degrees at many observation points around the metro area. A cold front should pass through Chicago early Wednesday, followed by a sudden turn to colder weather with falling temperatures.
Winter hits Chicago full-force Thursday
Winter storm warnings are in effect today over the southeast corner of Arizona, the southern half of New Mexico and extreme western Texas. Snow accumulations of 5 to 10 inches or more are forecast for higher elevations with several inches of snow possible even over lower desert areas. Current forecasts have the storm tracking through southern Texas and then northeast through Louisiana, eventually connecting with the cold front in Ohio and western Pennsylvania Thursday. The intensifying storm will pull cold air from the Canadian Tundra south into the Midwest. Thursday into Friday Chicago will experience strong north winds, snow showers and wind chills in the teens.
Dear Tom,
We have just returned from a visit to the Scilly Isles off the coast of extreme southwest England and we were astonished to see palm trees there. How is that possible?
The McCarthy Family, Chicago
Dear McCarthy Family,
It is astonishing, and it's a testament to the warming influence of the Gulf Stream. The Scilly Isles sit at 50 degrees North Latitude, as does Winnipeg, Canada, whose streets are definitely not adorned by palm trees. The Gulf Stream, which draws its origin from the warm waters of the Caribbean Sea 4,500 miles southwest of the Scilly Isles, trends northeast and powerfully warms the North Atlantic Ocean and, in turn, the air that gives Britain a climate far more moderate than its northern location might otherwise suggest. That said, Morton Arboretum dendrologist Dr. George Ware stresses that British palm trees are a more hardy breed than coconut-bearing tropical palms.
Tuesday marks the first day of meteorological winter (Dec.1-Feb. 28), and the following day winterlike weather is forecast to hit the metro area. After the sunny and mild Saturday when Chicago hit a high of 54 degrees and St. Louis came in with a 71 (just a degree below Miami, FL), the first three days of this week here are expected to average out about 5 degrees above normal. But the long-running mild trend that began in early November (the streak of above-normal temperatures reached 25 Saturday--tying the all-time record for November) will come to an abrupt end next Thursday. Low pressure moving northeast out of the southern Plains will merge with a cold front charging through the Midwest into the eastern Great Lakes, leading to a wintry mix over Chicago Wednesday with light rain changing to snow or flurries as temperatures fall.
A cold last half of the week
The first arctic air mass of the season will ride a strong northerly flow out of the Canadian Tundra directly into the western Great Lakes Thursday and Friday. In Chicago temperatures will fall into the 20s Wednesday night and fail to warm out of the 20s for the next two days, dropping into the teens overnight. With temperatures in the 20s and strong northwesterly winds gusting as high as 30 mph, Chicago's daytime wind chills will probably be in the teens both Thursday and Friday.
Dear Tom,
The rotation around a low pressure system is counterclockwise, when viewed from above. But when seen from the ground, the rotation appears to be reversed. Therefore, before we had modern radar imaging was the circulation described as clockwise since it was viewed only from the ground?
Carl Rollberg, Calumet Park
Dear Carl,
Wind circulation around low pressure systems (counterclockwise in the Northern Hemisphere) and around high pressure systems (clockwise) has always been described in the manner in which it is today because, when looking at weather maps or other displays of weather features (such as radar or satellite pictures), the view is always from above.
The sense of wind circulation around areas of low and high air pressure in the atmosphere first became apparent when meteorologists began to draw maps of weather features in the mid-1800s.
Chicagoans appear headed for what may be one of the final weekend encounters with 50-degree temperatures Saturday. The predicted 54-degree high would be the area's mildest reading since last Sunday. The air mass responsible produced 70-degree temperatures in the Plains Friday. There, such warming is amplified by the Chinook effect -- the compressional warming which occurs as winds descend from comparatively low mountaintop air pressures into the denser air found at lower elevations in the Plains. The compression of the air which results produces heating. The mild air which results ends up cooling a bit as it proceeds eastward into the Midwest but is still able to boost temperatures.
Readings at Saturday's 50-degree-plus levels are hardly a forgone conclusion this time of the year. Weather records reveal only slightly more than half (58%) of Novembers have produced 50-degree or higher temperatures in the month's final week over the past 138 years. We've actually been quite lucky this month. Saturday becomes November 2009's 19th day in the 50s -- well ahead of the 13 recorded in most Novembers.
But this weekend's meteorological nirvana suffers some real blows in the week ahead. A shot of colder air enters the area Sunday night and Monday while the season's most formidable blast of arctic air pours south into the nation's Heartland from mid-week on. There are growing indications temperatures will have to struggle to get close to 30 degrees once the frigid air arrives Thursday and Friday and that gusty winds are likely to restrict wind chills to the teens both days.
The one feature which may have to be monitored is a cut-off low aloft expected to dip into the Southwest this weekend then track slowly toward south Texas and the western Gulf of Mexico mid-week. Just how that system "opens up" (i.e. tracks to the northeast) will determine how an autumn storm -- expected to form south of the east Texas coast early next week -- impacts Chicago. At the moment, computer models have the system deepening impressively, with central pressures diving from 29.80" Tuesday evening to 28.88" by the time it reaches the St. Lawrence River in southeast Canada later Thursday -- but tracking east of Chicago. Any westward jog in this system's track next week would increase the storm's effect on Chicago.
Chilly rain or a rain/snow mix Wednesday morning could shift to a period of snow Wednesday afternoon and night before flurries ride powerful northwest winds into the area amid falling temperatures late Wednesday night and Thursday.
10 of 12 recent computer runs -- 83% -- indicate measurable snow here in the coming 2 weeks
Weather history puts the chance of measurable snow (0.1" or more) in December's opening week at 65% and the chance of an inch or more of snow at 43%. The odds may end up a bit higher this year if recent computer projections verify. Ten of the 12 most recent runs of the National Weather Service's Global Forecast System (GFS) forecast model -- 83% -- indicate the potential for measurable snow. An average of model snowfall estimates over the next two weeks comes to around 4" -- but individual model projections range from nothing to as much as 8.1" between now and Friday, Dec. 11.
Dear Tom,
Can you tell me in what compass direction the sun rises and sets in Chicago on the solstices?
George Berliant, Lincolnshire
Dear George,
On the approaching Dec. 21 winter solstice the sun will rise in Chicago about 32 degrees south of east and set 32 degrees south of west, giving the city just 9 hours and 8 minutes of daylight. Next June 21 on the summer solstice the city will enjoy its maximum daylight of 15 hours and 13 minutes of daylight with the sun rising about 33 degrees north of east and setting 33 degrees north of west. On the spring and fall equinoxes the sun rises directly in the east and sets due west. Triton College astronomer Dan Joyce marvels at how ancient Britons built the Stonehenge monument that not only perfectly aligned the seasonal sunrise and sunset positions, but also the more complex extremities of the moon.
Snow covered the ground -- but only briefly -- across some northwest suburbs early Thanksgiving morning. From Gurnee west to Algonquin, Huntley, Belvidere and Rockford and north into Wisconsin, the ground was white with a slushy covering of snow as Turkey Day got underway. There never was any question the snow's stay would be a short one. The warm ground and the brevity of subfreezing air temperatures there melted the snow quickly. 1.5" fell in Winnebago County's Roscoe while Hebron in McHenry County was hit by 1.3". Other totals included 1" at Belvidere and Woodstock, 0.5" Huntley, 0.3" Gurnee, 0.2" Fox Lake and De Kalb, and 0.1" in Elgin and several miles northwest of St. Charles in the Fox Valley.
There was no accumulation in Chicago or elsewhere in the metro area, though traces of snow were recorded at the Midway and O'Hare observation sites -- the 2nd time flurries have been in the air this season.
Thanksgiving parade-goers in downtown Chicago braved light rain and the area's chilliest weather in nearly 8 months. Thursday's 42-degree high was the city's coldest since April 6 when the high was 40.
The sun's back Friday, mixed at times with mid and high clouds. And while temperatures are likely to drop expeditiously with the setting sun Friday night, reaching the 20s in many areas away from the lake, generous sunshine and south winds promise to propel readings Saturday into the mid-50s -- a level 15-degrees above normal.
Arctic air's interaction with Gulf disturbance will have to be monitored
Saturday's warmth won't last. Modest cooling occurs once a front passes Sunday. And the area may be swiped by some chilly light rain mixed with sleet Sunday night. But far more interesting weather developments may loom later in the week. Early season arctic air appears likely to spill off the increasingly snow-covered Canadian tundra and into the Lower 48 Wednesday night and Thursday.
The wildcard in that transition revolves around a southern Plains and Gulf Coast disturbance expected to begin lifting northward mid-week. If southward-plunging arctic air manages to deepen an upper-air trough more than currently projected, the disturbance -- expected to spin up into a late autumn storm as it moves north from Alabama into Ohio -- could track farther west. This could bring snow on its northern flank into the Midwest Wednesday night and Thursday.
Dear Tom,
In Chicago, which month holds the record for the biggest difference between its highest and its lowest recorded temperatures. In other words, what time of the year can potentially bring the greatest temperature swings?
Jim Jacobs
Dear Jim,
With an incredible spread of 100 degrees between its highest and lowest recorded temperatures, March stands ahead of all other months. Chicago's temperature soared to 88 degrees on March 29, 1986, and plunged to 12 degrees below zero on March 4 in 1873. Respectively, those are the city's extreme temperatures in the month of March.
February and December, each with a spread of 96 degrees between their all-time highest and lowest temperatures, follow behind March.
The coldest half of the year brings Chicago its largest temperature swings, the warmest half of the year its smallest.
It's not pretty -- but it could be worse. Thanksgiving 2009 dawns with the Chicago area beneath a heavy overcast. The atmosphere has cooled overnight with computer models predicting the freezing temperatures, which began 2,500 feet above street level Wednesday evening, are likely to lower to 800 feet by daybreak. That's a level which would be low enough to allow at least a few wet snowflakes to reach the ground at some locations the first hours of Thursday morning.
Thanksgiving's high temperature is expected to hover between the mid-30s and 40 degrees -- the chilliest reading here in nearly 8 months. But the real chill occurs Thursday night as skies clear. With readings predicted to tumble into the 20s; the metro area appears in for the 2nd coldest nighttime temperature of fall 2009. It's possible normally colder locations may record low and mid 20-degree lows away from the city and the warmth of Lake Michigan.
Sunshine returns Friday -- but temperatures are to remain at typically chilly late-November levels, rising only to the low and mid 40s. Noticeable warming follows Saturday with gusty south winds propelling temperatures into the 50s -- nearly matching the levels observed last weekend.
It's chilly -- but still above normal; coldest air to hit 2nd half of next week
It feels chilly Thursday -- and the predicted daytime high of 40 degrees is to fall 2 degrees shy of normal high for the date. But with nighttime lows at O'Hare Airport likely to fall no lower than 30 degrees by midnight Wednesday night, the average temperature for the day is to end up above normal for a 23rd consecutive day.
Interestingly, Chicago's chilliest daytime reading since meteorological autumn began Sept. 1 has been 44 degrees. Only one year of the past 139 has failed to produce a colder daytime high temperature by Nov. 26.
Dear Tom,
I have a weather comment and a weather question. It seems as if Thanksgiving weather around here is usually lousy. That's the comment; here's the question: How often has it snowed here on Thanksgiving?
Richard Waller, Chicago
Dear Richard,
Taking into consideration the factors of weather that constitute inclement conditions -- such occurrences as overcast, blustery, gray, dreary and damp days, minimal sunshine, frequent and persistent precipitation -- Chicagoans endure "lousy" weather more often on Thanksgiving than on any other national holiday.
Chicago's snow season is barely getting under way in the closing days of November, but some snow (usually just flurries), has occurred on 41 of the past 133 years for which we have Thanksgiving snow data. However, an inch or more of snow has fallen on only seven occasions. The most: 3 inches in 1980.
The mildest November in eight years has managed to completely defeat snow production here. There hasn't been a single snowflake to date this month. The last flurries to fill Chicago's skies this season occurred more than a month ago on Oct. 16. The lack of snow places Fall 2009 among the 31 least snowy autumns to date over the area's 125 year observational record.
The situation could change a bit by Thanksgiving. Moderately colder air predicted to spill into the Chicago area Wednesday night and Thursday is expected to force freezing temperatures--situated more than 4,000 ft. above ground level as Wednesday dawns--closer to the ground at that time. It's a development which lowers freezing temperatures to within 700 to 1,200 feet above street level late Wednesday night into Thursday morning. Research suggests snowflakes are able to fall through a layer of above-freezing air up to 1,000 feet deep before melting---a fact which may well permit wet snowflakes to make it all the way to the ground for only the second time this season. The best chance of that happening is predicted to occur in a comparatively brief window from late Wednesday night into a portion of Thanksgiving morning---though cooling Thursday night may again allow flurries. Travelers need not worry the snow will stick. Temperatures are to remain above freezing as any flakes fall. That plus warm ground temperatures will prevent accumulations or icy road conditions. Even if an errant snow shower was to occur heavily enough to briefly coat the ground the snow, comparatively mild temperatures are likely to lead to rapid melting.
Latest at O'Hare without a temp colder than this fall's 28-degrees
This month's 47.1-degree average makes it the city's 10th mildest---5.4-degrees above the long term average. Wednesday's modestly cooler temperatures are unlikely to prevent it from becoming the 22nd consecutive above normal November day. The coldest temperature recorded this fall was the 28-degree low Nov. 12. Never in a half century of observations at O'Hare has the metro area been this far into the fall season without a colder reading on the books.
Dear Tom,
I've heard the sky is blue because of reflection off the oceans, but then why is the sky still blue over land?
Sheila Kelley, Montgomery, Ill.
Dear Sheila,
Our magnificent blue sky (which we've not seen much of recently) results not from reflection of light but from a process known as preferential scattering of sunlight.
Pure sunlight consists of a mix of all the colors of the spectrum blended together into white light, and each color has its own specific wavelength. As sunlight passes through the atmosphere to our eyes, the molecules of nitrogen and oxygen, the two gases that make up 99 percent of the atmosphere, separate ("scatter") the white light into its component colors.
However, this happens much more so for the shortest wavelength color -- blue -- than for the other longer-wavelength colors. Blue light is preferentially scattered and that is primarily what reaches our eyes.
Mild weather's had quite a run this month---but changes loom and it's possible snow flurries could be in the air here or nearby Thanksgiving (Thursday) for only the second time this season. Just a trace of snow is on the books here to date making 91 of the past 125 years---73 percent of them--- snowier by now. The comparatively quiet start of the 2009-10 snow season isn't limited to Chicago. An area of the Midwest well to the north---Negaunee Township near Marquette on Michigan's perennially snowy Upper Peninsula---has recorded only 3.3 inches of snow so far this autumn---the least snowy to date since records began there in 1961. It's a development which bears El Nino's imprint. El Ninos---which involve the warming of equatorial Pacific waters at the same time easterly Trade Winds weaken---have been known cut significantly into Midwest snowfall, though it's early in the season and a string of recent computer snowfall estimates suggest December could bring the Midwest a colder, more snowy period.
Despite Tuesday's damp, raw feel, the day is all but certain to post a surplus---becoming the 21st consecutive day to do so. To date, November 2009 is running an eye-catching 5.2-degrees above the long term (138 year) average---the mildest here in 8 years. The month's 47.2-degree average makes it Chicago 14th mildest Nov. 1-23 period of the past 139 years.
125 years of Chicago climate data show probability of snow on the rise this time of year
Though the area is past November 16th---the average date of Chicago's first measurable snow---climate data on the occurrence of snow here is clear. Snow begins occurring with increasing frequency from Thanksgiving forward. The holiday itself has recorded snow 41 of the past 133 years for which we have Thanksgiving snow data---31 percent of the time. Yet any snowfall on the holiday has generally been modest. On only 7 occasions has an inch or more fallen.
Though hardly universal--and not in a time range in which details of longer range weather developments can always be gleaned with great specificity---several computer models suggest December's opening week, which gets under way next Tuesday, could feature sticking snow. Weather records indicate an inch or more of snow has occurred in 40 percent of years and a half foot or more of snow has fallen 11 percent of the time during the period.
Dear Tom,
Why are wind directions generally parallel to the isobars on your weather maps instead of perpendicular to them, as the pressure gradients in that direction would warrant?
Robert Bacon, Darien
Dear Bob,
Air in motion (wind) is acted upon by two influences, the pressure gradient force and the Coriolis deflection. The former directs air from higher to lower air pressure, and this suggests wind should blow perpendicularly across isobars (lines of equal air pressure), from high to low air pressure, as you have indicated.
In the Northern Hemisphere, Coriolis deflects all moving objects (you, me, airplanes, ocean currents, wind) to the right of the intended direction. The net result of the two influences (pressure gradient and Coriolis) is that wind blows across isobars at an angle of about 30 degrees, always from higher to lower air pressure.
Not only has November been just about as warm as October was, but it's been much sunnier and far less rainy. The last three weekends have been absolutely spectacular with plenty of sunshine and balmy weather, and the city has not recorded a day with below-normal temperatures since Nov. 3. All that is about to change as the Thanksgiving holiday approaches. Colder weather will advance on the area beginning late Tuesday accompanied by some showers--and as temperatures plunge, snowflakes could mix with the rain by Wednesday evening and flurries could fly on Thanksgiving. No major cold or snow is on the immediate horizon, but the latest long-range computer forecasts into early December show a decided wintry trend.
Interior Alaska in mid-winter form
A early season cold wave of record proportions is gripping the interior portions of northern Alaska. Morning lows have dropped to 40 below zero or lower for six straight days in several areas, and highs have failed to top minus 30, shattering previous records for early season cold.
Dear Tom,
How does Lake Michigan affect Chicago's winter weather?
Erich Haupt
Dear Erich,
Lake Michigan has a large effect on winter weather in Chicago. Because of water's high specific heat, Lake Michigan is slow to cool in the fall, and this property often spares the city from early season snowstorms. As the storms approach the area the attendant east or northeast winds bring 40-degree-plus lake warmth inland, keeping precipitation in the city liquid or a rain/snow mix while snow piles up in the colder inland areas. In the same vein, mild flow off the lake can limit glazing during episodes of freezing precipitation. When arctic blasts invade the region, evaporation of lake moisture produces lake-effect rain or snow. Normally this precipitation targets northwest Indiana but will fall in Chicago when steering winds blow from the northeast.
With Sunday promising a repeat of Saturday's unlimited sunshine and mild temperatures in the middle 50s nearly 15 degrees above normal, Chicagoans are enjoying a third straight mild weekend.
While this weekend's highs in the middle and upper 50s pale in comparison to the back-to-back 70s on Nov. 7-8 and the 63-degree maximum on Nov. 14, the mild conditions will provide ample opportunity for end-of-season yard work or putting up holiday decorations. The balmy weather should last into Tuesday extending the current string of above-normal days to 21-the longest November stretch since 25 straight days were logged at Midway Airport in 1999.
Brief chill may bring snow
The warmth will not last through Thanksgiving as a cold front sends temperatures plunging late Tuesday. Showers should develop with the front and could mix with snow Wednesday as readings drop into the 30s. Thanksgiving looks to be cloudy with some flurries or mixed rain and snow possible with high temperatures struggling to reach 40 degrees.
Dear Tom,
In July 1987 while driving through the Mojave Desert on our way from Los Angeles to Las Vegas, heavy thunderstorms produced severe flooding and we were ordered off the road. How rare is this?
Kevin Vahey, Evanston
Dear Kevin,
It's not that rare. Rain is limited in the Mojave, averaging less than six inches a year. The desert's western flank receives the majority of its precipitation in the winter, while the eastern desert gets a substantial portion of its rainfall from summer thunderstorms in addition to the amount from winter storms. However, during the summer monsoon season, thunderstorms can form when moist air moves north out of the gulfs of Mexico and California. With ample moisture, strong heating and orographic lift provided by the mountains, the storms can bring blinding downpours.
Nighttime cooling has produced areas of low cloudiness and fog from moisture lingering in the wake of the past week's damp weather system. When temperatures lower at night, air masses grow saturated with moisture at the point readings match the dew point. It's the instant relative humidities reach 100 percent.
Despite areas of clouds, Chicago remains a safe distance from the country's major precipitation-producing weather systems over the pre-Thanksgiving weekend -- one on the Gulf Coast with big rains and another sweeping into the Rockies. It's a situation which should allow the weekend here to remain mild, further extending one of the longest spells of above-normal November temperatures on the books. Highs are to reach the 50s Saturday through Monday -- readings 10 to 15 degrees above normal and more typical of late October than November. The number of consecutive above-normal days reaches 19 Sunday, the 2nd longest such period at Midway Airport since weather records began in 1928. Only 1999 managed more -- 25 of them.
Though winds are light Saturday -- often an impediment to breaking clouds up this time of year -- computer models indicate the layer of moisture supporting Saturday morning's clouds is quite shallow. This should permit daytime heating to mix the air, dissipating the cloudiness and allowing generous sunshine to emerge. Hazy sunshine is likely to return both Sunday and Monday.
As additional evidence of how mild it's been of late, the coldest temperature recorded this fall has been 28 degrees, and the coolest daytime high this month has been 47. A vast majority of years have produced temperatures colder than each of these readings by now: 128 of the past 137 years have recorded a colder autumn low temperature by now, and only one year (1933) has seen its lowest November daytime maximum higher than this year's 47.
Changing pattern to send temps tumbling by Thanksgiving;
potential cold December open ahead
Many indicators continue to suggest large pattern changes loom over the next two weeks -- changes likely to send temperatures broadly lower over the United States. The colder air appears likely to hit in two waves -- and there may be temporary warming between them.
Cold weather surges into the Midwest on gusty winds Tuesday afternoon and Wednesday amid chilly showers. Readings may be chilly enough to allow at least some mixed snowflakes to the reach the ground with the spells of cold rain. The chilly air is likely to hold Thanksgiving temperatures near 40 degrees. Even colder air may hit next weekend and carry into December.
Dear Tom,
On the evening of Aug. 10 I was checking the weather for many cities coast to coast and they were all 79 degrees. Is that rare and is it more likely to occur in summer?
Norman Alexandroff
Dear Norman,
Having a large expanse of uniform temperatures across the nation is quite unusual and would be far more likely to occur in summer than any other time of the year. Temperature contrasts are almost always greater in the winter with arctic air and snow cover much more frequent across the northern states. Summer's sluggish weather patterns are more conducive to smaller temperature ranges -- especially at night when sunshine is not a factor. Conditions that would bring similar temperatures on a regional basis are far more common and can occur throughout the year given the right conditions.
Friday marks the 17th consecutive day of milder than normal temperatures in Chicago--one of the five longest such spells on record in the month of November at Midway Airport. Weather observations there date back to 1928. With above normal readings expected to continue into early next week, the mild spell is on track to become this area's 2nd longest of any November. That so many above normal days have occurred is likely to surprise many Chicagoans. A heavy, week-long overcast peppered with bursts of light rain and, until Thursday, wind chill-generating gusts, have contributed to a much cooler "feel" to the air than readings alone might indicate. The month's 47.5-degree average temperature at O'Hare is the 20th warmest of the past 139 years, placing the month among the Chicago area's 14 percent of mildest Novembers. Estimates based on temperatures suggest furnace usage should be down 25 percent over typical levels up to this point in the month and 18 percent below the same period a year ago.
A stubborn low pressure responsible for five consecutive days of cloudy skies has lifted out of the area--but, moisture lingers in its wake. And, while clouds may break for passing sun in coming days, spells of overcast skies aren't likely to exit the area completely--fitting in a month which is historically the second cloudiest of the year (December is the cloudiest).
Daytime temperatures are predicted to rise several degrees in each of the next three days. But, indications of change in the weeks ahead abound. Two key cold weather indexes, which look at cold air availability in the arctic as well as the predicted buckling of the jet stream over the North Atlantic---a development which frequently ends up sending cold air spilling southward over the eastern U.S., including the Midwest---have turned negative. It's an indication of colder weather on the way. The chill appears likely to hit in bursts---the first to produce a rain-generating disturbance here late Monday into Tuesday. That push of cold air is to last through through Thanksgiving (next Thursday) and may deliver this area's coldest readings of the season to date. There are growing indications flurries or snow showers could sweep at least parts of the metro area Wednesday and Thursday. Still colder air appears a threat as December hits 12 days from now. That chilly spell could allow some sticking snow at some point in December's opening 5-days, according to several preliminary computer forecast scenarios.
West Coast hit by driving rains, huge mountain snows, 100 mph wind gusts
The storm pounding the West Coast Thursday has prompted warnings for all manner of extreme weather---from heavy rain and flooding, to mountain snows measured in feet, and high winds responsible for huge waves lashing the coastline. Gusts hit 103 mph at Rogue Valley International Airport near in southern Oregon near Medford Thursday.
Dear Tom,
I was married on Dec. 8, 1945 and it was a very warm day. A week later when my friend got married on Dec. 15 it was below zero. Can you provide the details?
Delores Faltynek Antioch
Dear Delores,
We asked climatologist Frank Wachowski to check the weather archives and he found your recollections to be right on---illustrating how quickly Chicago weather can change this time of the year. You wedding day was indeed very mild with a balmy high of 53 degrees. Your friend was not as fortunate as winter hit with a vengeance in the following week. A cold front dropped temperatures into the 20s and a major snowstorm followed on Dec.13 and 14 bringing about 4 inches of snow. Your friend's Dec. 15 wedding took place on a very wintry day with a high of just 11, a low of 2 below zero and 4 inches of snow on the ground.
Clouds cover area skies a 5th consecutive day Thursday and periods of rain are to continue. Wednesday's 0.17 inches at O'Hare made it the wettest day since late October. The day's 47-degree peak reading was the third consecutive day in which temperatures failed to escape the 40s. With a fourth day of 40s predicted Thursday, the metro area is in the midst of its longest cool spell since a set of seven consecutive 40s Oct. 10-16.
To say it's been dreary is a bit of an understatement. Chicagoans have seen only 1 percent of the area's possible sun since Sunday---and November, typically the second-cloudiest month of the year here, is showing every sign of living up to its cloudy reputation over the coming week. The sluggish storm which has spun in place all week shrouding the area under a veil of clouds, is finally to lift out of the Midwest Friday. But computer models hold a fair amount of moisture in the lowest 5,000 feet of the atmosphere in the wake of the departing storm. This is more than adequate to produce clouds and could make sunshine a comparatively rare commodity. What's more, suggestions that a wet new storm is to come together across the Midwest Monday is hardly a boon to those in search of sun. Though the details of its development aren't yet carved in stone, a number of forecast scenarios predict strengthening over eastern Iowa and Missouri Monday, leading to the onset of chilly rains in Chicago Monday night and Tuesday.
Temperatures over much of the coming two weeks remain above seasonal norms, but display a downward glide. One lobe of chilly air is likely to be drawn into the Midwest on the blustery backside of next week's storm, producing a cool Wednesday and Thanksgiving Day. It's possible mid-week cooling will be sufficient to introduce snow or rain showers. But even colder air may loom beyond that. Though temperatures are likely to moderate after Thanksgiving (next Thursday,) preliminary indications suggest December---which is just 13 days away--may open on a wintry note as even colder air descends into the Chicago area.
Historic odds of a trace or more of snow falling in November's 12 remaining days: 88 percent
The possibility of snow grows this time of year. Snowfall records in Chicago extend back 125 years to 1884. At a least a trace of snow has fallen in 88 percent of those years between now and the start of December. Measurable snow (0.1 inches or more) has fallen in the same period in 60 percent of years and an inch of snow has fallen by December first 38 percent of the time.
Dear Tom,
I am putting in a bid for sidewalk snow removal in the Lincoln-Belmont-Ashland shopping area. Can you provide the average frequency of the number of snows per season of various amounts?
Bill Haderlein, Chicagoland Deck Cleaning & Sealing
Dear Bill,
Indeed we can. The following statistics are derived from 80 years (1929-2008) of Midway Airport snowfall data, courtesy of Chicago weather historian Frank Wachowski.
On average, Chicago receives at least one-half inch of snow 17 times per snow season. Snow storms in the range of 1-3 inches occur about 7 times; 4-6 inches, twice; 7-10 inches, once; more than 10 inches, about once every other year.
A note of caution: The number of storms that might occur in any given snow season varies greatly from year to year. The extreme winter of 1978-79 put down 10 snows in excess of 4 inches and a season total of 89.7 inches.
Chicago's weather has turned wet for the first time in over two weeks bringing to an end the driest November open in a decade. Just 0.01 inches had fallen in the city up to the time rains arrived Tuesday afternoon. Rainfall is predicted to continue in waves through Thursday totaling 0.40 to 1 inches making it the area's heaviest spell of precipitation in the 18 days since 0.81 inches fell October 30.
Northeast winds, so successful in halting the northward spread of rain Monday, proved no match for the deep-layered surge of moist air which pushed rain into the metro area by Tuesday afternoon. The most impressive area totals ranged from 0.91 inches at Rensselaer and 0.71 inches at Hebron, both in northwest Indiana---to 0.61 in De Kalb County's Sandwich. Chicago rains, while enough to wet the pavement, weren't nearly as impressive---totaling just 0.08 inches at Midway and 0.05 at O'Hare---but more was expected to fall overnight.
The stalled low pressure system responsible for the wet weather is a "cut-off low." The term originates from the fact the strongest upper levels winds, which might otherwise push such a disturbance along, become situated well to the north. Systems spin in place when this happens, unable to move very quickly. The varied barometric pressures on the storm's north side were behind Tuesday's howling northeast wind gusts which approached 40 mph here and limited wind chills to the low and mid 30s.
Areas downstate bore the brunt of storm's rainfall for a second consecutive day. Totals there were impressive. Westville in east-central Illinois' Vermillion County just east of Champaign recorded 3.23 inches of rain while Lincoln was soaked by 3.14 and Danville was hit by 2.45. To put those amounts in perspective, the entire month of November in Chicago typically sees 3.01 inches.
Alaska in the Deep Freeze; Interior temps drop under -40 degrees
Cold air has reached brutal proportions in the northernmost reaches of North America. Temperatures in Alaska dropped to -45 degrees at Tanana--in the state's Interior not far from Fairbanks Tuesday, to -44 degrees at Bettles. Open water in southern Alaska appeared to "steam" as the bitterly cold air turned water vapor immediately to ice crystals, much as happens when brutally cold air makes contact with the "warmer" water of Lake Michigan here in winter. Days continue to shorten in across the northern hemisphere assuring cold air production is just beginning in the arctic. The sun sets in Barrow, Alaska Thursday for 64 days---not to rise again until late January.
Even where the sun is still visible during the day well to Chicago's north, it sits low in the sky. At its highest point Tuesday, the disc of the sun was just 6.1 degrees above the horizon in Fairbanks compared to 29 degrees above the horizon at its peak here in Chicago. (Note: Were the sun 90 degrees above the horizon, it would be directly overhead while a sun angle of 0 degrees means the sun's disc sits below the horizon.)
Dear Tom,
What are the extremes for Chicago's average annual temperatures? Any sign the average is rising due to global warming?
Robert Roschke, Chicago
Dear Robert,
In 138 years of official data, Chicago's average annual temperatures have ranged from 45.3 degrees (1875) to 54.5 degrees (1921). The trend of temperatures has been upward, but it's difficult to draw conclusions because the observation site has been relocated several times and each move disrupted the climatological continuity of the temperature record.
However, 80 years of data (1929-2008) from a single location -- Midway Airport -- indicate a warming trend, probably due more to a strengthening urban heat island effect than to global warming. Annual temperatures rose from 50.6 degrees during the first half of the period (1929-1968) to 51.2 degrees during the second half (1969-2008).
Sections of downstate Illinois, including the St. Louis area, were drenched by 1 to 2-inch rains Monday at the same time a foot of heavy, wet early season snow snapped power lines near the Nebraska/northeast Kansas border just northwest St. Joseph, Missouri. Morrowville, Kansas was hit by 12 inches of snow while rainfall in the storm's mild eastern sector reached 2.01 inches at downstate Fairview Heights, Illinois and 1.62 at St. Louis. The storm responsible is behind the powerful east to northeast winds which continue to rake the Chicago area Tuesday morning and produced 30+ mph gusts here Monday. With origins in Canada, the dry low level flow proved a formidable barrier to the northward spread of the storm's rain. While northwest Indiana's Hebron recorded 0.22 inches of rain and 0.10 fell at Valparaiso---both in Indiana-- just 0.01 inches fell at Midway with a trace at O'Hare.
The wet storm, spinning in place over Missouri late Monday, is mired in an atmospheric blocking pattern which has the system, for all intents and purposes, spinning in place. Since any forward motion isn't expected to resume until late this week, it's likely the storm's impact on Chicago's weather has days to run. Computer models suggest the dry air riding Monday's northeast winds into the area is to moisten slowly allowing rain prospects to rise. Once the atmosphere becomes saturated later Tuesday and Tuesday night, the rainfall which results could linger through Thursday.
While the air is to take on an increasingly damp, raw feel, temperatures are actually running above November averages. Winds and clouds are interfering with normal nocturnal (nighttime) cooling, a development which contributes to daily temperature surpluses. Tuesday marks the 14th consecutive of above normal November temperatures---and each day over the coming 7 days appears likely to finish ABOVE normal as well.
Changes loom Thanksgiving week; signs of colder temps and more storminess
Important atmospheric changes appear to loom next week. A dome of milder than normal air is predicted to take shape over eastern Canada and the Davis Strait between Labrador and Greenland. Such a development often signals a surge of cool air into eastern North America as the continent's jet streams begin buckling. Ridging in the jet over the western Atlantic is offset by troughing in the eastern U.S. which produces northwest steering winds above the Midwest--a flow able to tap cold air at higher latitudes and tug it south. Two storm systems may be by-products of this pattern evolution and an analysis of temperatures suggests readings by the end of next week and the following weekend may dip 15 to 20-degrees below the levels predicted later this week.
Such a pattern change isn't out of line with typical late November developments. 125 years of snow records here reveals the week leading up to Thanksgiving has produced at least a trace of snow 74 percent of the time while measurable snow (0.1 inches or more) has fallen in 42 percent of all years since 1885.
Dear Tom,
With winter approaching, how soon can we expect temperatures to drop below
zero?
Myra Weisbach
Dear Myra,
Chicago¹s earliest encounter with subzero weather took place nearly 60 years ago on the frigid Thanksgiving morning Nov. 23, 1950 when the mercury plunged to 1 below. The next day was even colder, with a low of minus 2 degrees. Subzero cold that early in the season is unusual, with the bulk of the city¹s negative temperatures occurring from mid December through mid February. The frigid season in Chicago peaks during February¹s opening days, a time of year that coincides with the winter¹s most persistent snow cover. Early March usually marks the end of below zero weather, though the 1 below zero reading on March 22, 1888 is the latest on record. Last winter Chicago logged 10 below zero days--the coldest was a minus 18 on Jan. 16.
Dear Tom,
If I throw a bucket of water from a hot air balloon at say 15,000 feet, will this water appear as rain drops or as big globs when it approaches ground level?
Don Sadecki, Westchester
Dear Don,
You'll get raindrops at the ground. Larger drops fall faster than smaller ones, but drop size has an upper limit. It's a matter of drop stability.
German physicist Dr. Philipp Lenard made the first accurate measurements of raindrop sizes, shapes and fall speeds around 1900. He found that raindrops can attain sizes no greater than one-fifth inch in diameter; they become unstable and shatter at larger diameters, and the largest drops fall at about 20 mph.
As a large raindrop falls faster and faster, the friction of its passage through the air causes it to flatten, then to bulge upward in the middle rather like an inverted paper bag, and finally to shatter into smaller drops that fall more slowly.
Most locations received little more than a few sprinkles or brief showers late Saturday afternoon and overnight as a cold front moved through, but Chicago's long dry period that extends back to the last day in October is about to end. Low pressure is expected to develop over Missouri Monday and ever so slowly work it's way north and east through Illinois, finally weakening as it reaches Wisconsin and Michigan later in the week. Rain is forecast to move into the Chicago area possibly as early as later this afternoon and then continue overnight into Monday. The slow-moving low pressure portends an extended period of cloudiness and off-and-on showers through Thursday.
Above normal temperatures to continue
The clouds and rain ahead should cut back considerably on the range of daily temperatures with readings holding for the most part in the 40s through mid-week. So even though it will feel cool and damp to Chicagoans, daily average temperatures will be in the middle 40s, some 5 degrees above normal for mid-November. Beginning on November 4th, average daily temperatures at the O'Hare official observing site have been above normal. A warm-up is forecast the latter half of this week and seasonably mild readings could extend well into Thanksgiving week.
Dear Tom,
What is Chicago's longest string of daily lows at 10 degrees below zero or lower? What about zero or lower? And what is our longest string of highs 90 degrees or higher? What about 100 or higher?
Lou Liebovich, Hoffman Estates
Dear Lou,
Computer scans of three data sets -- Chicago's official temperatures (1871-2009) and data from Midway Airport (1928-2009) and O'Hare International Airport (1959-2009) --provide the answers. Chicago's longest string of days with low temperatures of 10 degrees below zero or lower is 7 days (Jan. 14 to 20, 1994); zero or lower: 10 days (Jan. 4 to 13, 1912, and Jan. 2 to 11, 1979); highs at or above 90 degrees: 12 days (July 6 to 17, 1936). That 90-degree string also included the city's longest string at or above 100 degrees: a sweltering 8 days (July 7 to 14, 1936.
Rain's been a scarce commodity in November but is threatening a windy comeback. Only 0.01 inch has fallen over the past two weeks, quite a change from an October in which 23 of the month's 31 days hosted at least a trace of rain. It's been the driest open to a November in a decade.
The rain's return is likely to begin quite modestly late Saturday night as post-frontal sprinkles build to a few light showers behind a wind-shifting cold front -- pause Sunday morning, then increase in number and coverage Sunday afternoon and night. Computer model handling of the wet system's movement into next week has been stunningly inconsistent in recent days -- potentially impacted by the massive Mid-Atlantic storm responsible for three days of driving rains and punishing winds in the region. Gusts Friday peaked at 60 mph at Cape May and 58 mph at Atlantic City -- both on New Jersey's coast. Gusts hit 56 mph at Ocean City, Md., and roared across Brooklyn, N.Y., at 47 mph. Air ascends into the atmosphere on a massive scale in storms as powerful as this one, forcing upper steering winds to flow around it. Such a split in the winds at jet-stream level can have continental weather implications, slowing the eastward progression of weather features. There is little doubt the storm has played a key role in slowing mild air's arrival here in recent days -- and, now that it's here, is likely to slow its retreat until Sunday's predawn hours.
Most aggressive among a suite of computer projections sweeping rain into Chicago, then holding rainfall in place for up to 5 days (through Thursday), has been the global forecast model run by the European Medium Range Forecast Center. The model generates precipitation totals approaching 2 inches and suggests the storm responsible is to lift from New Mexico and the Texas Panhandle into southwest Missouri by late Sunday, and then into downstate Illinois Monday. There, the system stalls as the upper air low producing it separates from powerful jet stream winds which might otherwise push it along.
Wet weather would be bad news for area farmers, who in recent weeks have finally been able to make progress harvesting crops. Veteran Will County farmer John Hazzard reported late Friday that most soybeans have been harvested -- but only 10 percent of the corn crop has been taken out in the hope further drying may occur. Corn moisture is well above normal, and harvested corn must be dried at the elevators to which farmers take their crop -- a slow process because elevators are able to process only so much corn on a given day. Hazzard reports yields have been good but estimates the corn harvest may take many weeks to complete.
Weather history indicates a majority of years see at least some measurable snow between now and Thanksgiving
Frigid arctic air gripping northwestern sections of North America and responsible for subzero temperatures in northern Canada and sections of Alaska in recent weeks, has shown little inclination to pour south in any great quantity. But longer-range projections are hinting that may change -- and it could happen toward the end of the coming two weeks during Thanksgiving week. A ridge forecast to build over Greenland at that time favors model projections of jet stream buckling over North America which would bring colder air crashing into a large swath of the Lower 48. Weather records show cold air before November's close isn't unusual and that 62 percent of all years since snow records began in 1884 have recorded measurable snow between now and Thanksgiving.
Dear Tom,
My 5-year-old asks when the dinosaurs disappeared and if weather was the cause.
Jennifer Krause
Dear Jennifer,
Five major "life extinctions" have occurred on Earth, one of which ended the reign of the dinosaurs about 65 million years ago (though recent evidence suggests some dinosaurs survived and today's birds are descended from them).
A widely accepted theory to explain the dinosaur extinction draws together information from a variety of independent investigations. An asteroid estimated to be 6-10 miles in diameter crashed into Mexico's Yucatan Peninsula. The impact threw a massive amount of debris into the atmosphere, and heat generated as it rained down planetwide caused much of Earth's vegetation to burn. Volcanic eruptions elsewhere contributed additional atmospheric dust, and temporary global cooling hastened the dinosaur extinction.
It was like a scene out of the Perfect Storm on the East Coast Thursday. Torrential rains---in spots more than 9 inches of it---fell horizontally as easterly winds roared ashore up and down the Mid-Atlantic Seaboard from New England to North Carolina at speeds found only in the region's most potent storms. NOAA offshore buoys bobbed about in mountainous three-story waves as shoreline cameras captured scenes of oceanic chaos as swarms of frothy waves lapped ominously at sand dunes and buildings normally out of the water's reach---but in harm's way Thursday as relentless east winds pushed a dome of Atlantic water over the shoreline at levels not seen in 13 years. The stormy environment, a by product of Hurricane Ida's remnants interacting with a sprawling Canadian high pressure, appears to have contributed to the disappearance of three commercial fishermen off Cape May, New Jersey. A 19 hour air and sea search for them was called off at 5 p.m. Virginia Governor Timothy Keane declared a state of emergency and urged people in the hardest hit areas of his state to stay home as power lines fell and standing water closed roads. Among the areas in Virginia hard hit by flooding was the Norfolk area.
Wind speeds were stunning. A Weather Bug sensor clocked a gust of 106 mph around 11 a.m. Thursday morning on the beach at Ocean City, Maryland while another nearby captured a 91 mph gust. Winds reached 68 mph at Fenwick Island, Delaware, 67 mph at Virginia Beach and 65 mph at Norfolk---both in Virginia---and 56 mph farther north at Atlantic City.
Rainfall surged past 9 inches at some locations. Swansboro, North Carolina was socked with 9.26 inches of rain while 9.12 soaked Jones Creek, Virginia.
Paltry November rains here lowest in a decade, 5th lowest on record
The East Coast storm appears to be contributing to a slowdown in U.S. weather movement---a development which could extend the 60s predicted Friday into Saturday. And while a chilly, wet storm is predicted by models to lift into the Midwest Monday, Chicago's paltry 0.01 inches tally this month is the lowest in a November in a decade and the 5th lowest of any November over the past 139 years.
Dear Tom,
On Nov. 11, 1911 Springfield. Missouri experienced a huge temperature drop attributed to a "Great Blue Norther." Can you elaborate?
Les Herbst Lake Villa
Dear Les,
A "Blue Norther" is a fast-moving cold front accompanied by a strong north or northwest winds, a dark blue-black sky and a large, rapid temperature drop. Such was the case on Nov. 11, 1911 in Springfield, Missouri when the cold front passed. Earlier in the day, with clear skies and brisk south winds, the temperature soared to a record high of 80 degrees. Around 3:30 p.m. dark
ominous clouds rapidly approached followed by an abrupt wind shift to the northwest. Sustained winds of 54 mph and gusts to 74 mph damaged numerous trees and houses. Temperatures plunged, falling to 13 degrees by midnight, setting a record low for the day. Nearly a century later the record low still stands, but the 80 degree high was equaled in 1989.
Temperatures appear likely to surge within striking distance of 60-degrees Thursday and into the mid to upper 60s Friday afternoon. Cloudiness plays a key role in the extent of daytime heating which takes place this time of year. November's lower sun angle means any interference by clouds can limit warming. The expectation that cloud cover here over the next two days will be of the high, thin variety underpins our prediction of 60-degree readings. High clouds tend to interfere less with sunlight than denser low clouds. The predicted parade of 60s may even extend into a third day Saturday before a wind-shifting cool front passes, swinging winds around to the northeast off Lake Michigan. That plus a thick, occasionally showery overcast is likely to allow a flood of cooler air into the area which, along with predicted rain Sunday, should lead to a much cooler back half of the weekend.
Highs in the 60s become less frequent from this point forward each year. An average of four 60s have occurred beyond Nov. 12 in the past 138 years. By contrast, freezing temperatures grow more numerous. Weather records reveal only 7 percent of the Chicago's 32-degree or lower temperatures have typically occurred by now.
A howling northeaster (or nor'easter) pumped 50+ mph wind gusts into sections of the Eastern Seaboard Wednesday. Gust hit 57 mph at Ocean City, Maryland. The storm--which combined the remnants of Hurricane Ida with widely varied pressures beneath the southern flank of a sprawling high draped from the Midwest to New England, produced the roaring winds which set in motion seething, white-capped surf conditions from the Carolinas north to the Delmarva Peninsula. The system's driving rains drenched a multi-state region and totaled nearly 10 inches (9.83) at Opelika, Alabama.
Far to the northwest a powerful storm in the Bering Sea sent 70 mph hour gusts across western Alaska. Forecasters warned 65 to 90 mph gusts could sweep the Turnagain Arm southeast of Anchorage in the south-central section of the state. As much as 10 to 20 inches of snow was predicted in the Susitna Valley south of the Alaska Range.
75 percent of the past 138 years have produced a colder temp by now
Chicago's coolest temperature to date has been 29-degrees recorded on Oct. 11. Three quarters of all years since 1871 have produced a colder reading by Nov. 12.
Dear Tom,
With the holidays approaching I remember a big Thanksgiving Eve snowstorm that probably was in the middle 70s. What year was that?
Ray Consentino, Homer Glen
Dear Ray,
The storm you remember took place on Nov. 26-27, 1975. The snow began Wednesday afternoon and fell with increasing intensity throughout the evening rush hour. The heavy snowfall clogged highways and canceled flights paralyzing holiday travel. Snowfall that Wednesday totaled 7.5 inches, and when the snow finally ended on Thanksgiving morning the city's official site at Midway Airport had logged 8.6 inches of snow. On Thanksgiving morning the snow was eight inches deep, tying 1895 for the city's deepest Thanksgiving snow cover. Just five years ago, another traffic-snarling Thanksgiving Eve snowstorm dropped 4.3 inches on Nov. 24, 2004.
Friday is to be the mildest of the coming 7 days though highs Wednesday and Thursday are to exceed the normal maximum of 49-degrees. Wednesday's initially chilly readings---the product of cooling beneath clear skies and light winds overnight---should give way to mid 50s fairly expeditiously beneath the sunniest skies here in three days.
November's temperature turnaround has caught Chicagoan's attention. Readings are averaging 4.5-degrees above the month's long term average, and, in an uncommon development, continue warmer than October. Generous sunshine again Thursday may well foster near 60-degree highs.
Changes have been made to the coming weekend's forecast including lowering predicted high temperatures and introducing the chance of some rain---though a majority of hours this weekend are still expected to remain dry. Details of the system which may produce at least some of the weekend rain Sunday still vary among models. This suggests a forecast situation still subject to change. But, the unifying conclusion of all models is that cooler air is to settle in, dampening hopes this weekend will be anything near as warm as last with its 70-degree highs. Several computer projections indicate frontal waves capable of instigating showers Sunday---while two others are the most aggressive in developing rainfall here. These forecasts suggest a windy storm will develop over eastern New Mexico and the Texas Panhandle Saturday evening then advance to Missouri by Monday morning and to central Illinois and Indiana by Monday evening. Such a scenario would lead to a classic autumn storm, with a thick, temperature-restricting overcast, strong east/northeast winds and impressive rainfall. But this solution is hardly unanimous and will have to be monitored in the days ahead.
Ida swamps Southeast with local 7-inch totals, 50+ mph gusts
Rainfall across sections of the Southeast with Hurricane Ida's remnants Tuesday reached 6.74 inches Gonalez, Florida and 6.61 at Foley, Alabama while winds gusts hit 54 mph at Mobile, Alabama and 52 mph at Pensacola, Florida. Heavy rains extended north into the Carolinas and powerful winds in coming days resulting from the widely varied pressures between Ida's remnants and a sprawling high pressure to the north are expected to produce easterly gales near Washington, D.C. south to the Carolinas. Waves are likely to top 20 feet there.
Dear Tom,
My family visited Glacier National Park in July and a park ranger said the glaciers were in retreat. Could you provide more information?
The Stein family, Chicago
Dear Stein family,
U.S. Geological Survey researchers are carefully monitoring the disappearance of glaciers and snowfields in Glacier National Park and they indicate that it is occurring quickly.
One report, prepared in 2008, says, "Glaciers don't respond to anything else except climate change, unlike, for example, forests that can adapt. ... In 1850 there were an estimated 150 alpine glaciers of 25 acres or larger (in the park). Now there are only 25 glaciers left. By 2030, computer models suggest that all the remaining glaciers and snowfields will be gone."
Park snowfall has increased 10 percent in the past 50 years, researchers say, but higher temperatures and melting have overwhelmed the heavier snows.
In most years, ever-shorter days and lowering sun angles assure November ends up cooler than October. But not this year. The weather of Autumn 2009 continues its unusual ways. Buoyed by this past weekend's back to back 70s---71-degrees Saturday and 70-degrees Sunday---November's opening 9 days have averaged 0.5-degrees milder than October's full-month average of 48.8-degrees. That's only happened in 12 of the 139 years on record since 1871. One has to go back 22 years to find the last time a November opened warmer than October.
Putting two consecutive 70-degree temperatures together this late in the season is unusual enough. Not since 1999---and before that 1971---has that happened in Chicago over the past half century.
A sprawling high pressure, draped from the Plains to the Northeast U.S. and Canadian Maritimes, is behind Tuesday's cool, occasionally gusty northeast winds here in Chicago. But it is also acting to block the northward spread of moisture accompanying Tropical Storm Ida.
Though not directly responsible for the deadly downpours which set in motion the devastating mudslides responsible for 130 deaths across El Salvador in recent days, there's little doubt Ida played a role in enticing prolific rains with a tropical Pacific system into the Central American country. Ida, with a circulation disrupted by the mountains of Nicaragua and Honduras late last week, returned to hurricane status quickly once the system moved over the bathtub-warm waters of the Caribbean and southern Gulf over the weekend. The system's northward drift over cooler northern Gulf waters sapped some of Ida's wind energy Monday---though the powerful low pressure's rain-generating capability is to remain formidable in coming days. A slowdown in its forward movement is an ominous development for the Southeast---including the southern Appalachian region---where repeat downpours make local 6 to 8-inch rains all but a certainty.
The variation in pressure between Ida and a huge Canadian high to the north produced gusty winds across much of Florida and northeast Gulf Coast Monday. Peak gusts reached 52 mph at the Tyndall Air Force base control tower, 49 mph at Sand Key, 44 mph at Pensacola, 42 mph at Hollywood--all in Florida. Rainfall by late evening had surged to 3.45 inches at Pensacola, 2.79 at Pascagoula, Mississippi and 2.77 at Saraland, Alabama---just the beginning of the wet weather expected to linger in the region as Ida's remnants slow.
Dear Tom
Someone told me that Lakes Michigan and Huron are really one lake. Is This true?
Ken Cleys Woodridge
Dear Ken,
Though they have long been, and will always be considered to be two different lakes, geologically and hydrologically, Lake Michigan and Lake Huron are actually one lake joined at the Straits of Mackinac. They lie at the same surface elevation of 577 feet, both lakes' level rise and fall together and flow of water between the lakes can reverse through the Mackinac Straits.
Great Lakes' water levels reported by the Great Lakes Environmental Research Lab and the U.S. Army Corps of Engineers provide only one reading for the Michigan-Huron duo. Because of their large size, early explorers gave the lakes different names. Combined, lakes Michigan and
Huron would cover more than 45,000 square miles, larger than Lake Superior's nearly 32,000 square miles.
Coming off a delightful late fall weekend that brought the city its first back-to-back 70-degree days since Sept. 24-25, prospects for mild weather here loom well into mid-November. With a prevailing west-to-east jet stream promising to spread mild Pacific air across much of the nation for the next two weeks, arctic air should remain bottled up across this continent's polar regions. Readings here should fluctuate through the 50s and 60s -- well above current normal temperatures around 50. While this weekend's 70s did not break any records here, new record highs were established Sunday in areas from Michigan to New York, including 72 at Grand Rapids and 71 at Muskegon, both in Michigan.
Category 2 Ida heading for Gulf Coast
A lackluster 2009 hurricane season has become active in its final weeks. A hurricane watch has been posted for the Gulf Coast from eastern Louisiana to the Florida Panhandle as Ida, packing top winds of 105 mph, approaches the area by Monday night or early Tuesday. Ida's death toll is approaching 100 in El Salvador after three days of flooding rains there.
Dear Tom,
From Nov. 12-14, 1964, Chicago firemen battled numerous multi-alarm major fires. What were the weather conditions like?
Doran Swan, Chicago
Dear Doran,
The weather was windy, dry and unseasonably warm -- perfect conditions for fires to spread rapidly and burn out of control. Chicago climatologist Frank Wachowski found high temperatures reached the 60s on Nov. 11-12 and peaked at 71 degrees on the 14th. Afternoon humidities fell to near 30 percent and winds were strong and gusty from the south and west with a maximum gust to 59 mph on Nov. 12. Three of the biggest fires were at the old Goldblatt's warehouse at 4000 S. Kedzie, buildings near 25th and Michigan, and in an abandoned railroad warehouse near 18th and Clark. Wachowski noted that weather reports from Midway Airport reported heavy smoke northeast of the field.
After a cloudy, chilly and rainy October that failed to produce an official 70-degree high in Chicago for the first time since 1917, the city is finally getting some October-like weather in November. Afternoon highs are slated to break the 70-degree barrier again Sunday as southerly winds carry the late-season warmth into the city. The warm weather is expected to linger into Monday, bringing the city four straight days of 60-degree-plus highs, an occurrence logged this late in the season at Midway Airport only 13 times since 1928. In addition to the return of warmth, Chicago is also drying out after an October that produced precipitation on 23 of the month's 31 days. In contrast, November's opening week produced just one day with rain -- a mere 0.01 inch.
Ida regains strength
Hurricane Ida weakened to a tropical depression after a Nicaragua landfall, but is expected to regain hurricane strength Sunday as it pushes north into the Gulf of Mexico. It could bring rain and strong winds to the Gulf Coast by Tuesday.
Dear Tom,
I was just a kid but I think I remember a big snowstorm that occurred just after Halloween. It must have been in the early 1950s. Am I correct?
Brian Schwartz
Dear Brian,
The year was 1951 and the first week of November featured two major snowstorms. Halloween was a chilly affair with highs only reaching the lower 40s. A surge of cold air followed and held the mercury to just 29 degrees on Nov. 2, setting the stage for a fast-moving Alberta Clipper that dumped 4.4 inches of snow on the city during the afternoon of the 3rd. That was just the beginning as a second, more powerful snowstorm hit on Nov. 6-7, bringing another 9.3 inches of snow. That storm was accompanied by howling northeast wind gusts to 65 mph at the lakefront Meigs Field airport. The winds produced high waves that brought major flooding and property damage along the lakefront.
The warmest weekend in six weeks is underway. Chicago area temperatures broke above 60 degrees for the first time in a week Friday, reaching 62 at O'Hare and Midway airports, and 63 at the lakefront. Among the warmest area highs Friday were 65 degrees at Rockford; 64 at Aurora and DuPage Airport; and 63 degrees at La Grange, Wheaton, Lansing and Plainfield.
Weekend readings look even warmer: A pair of 70-degree highs (or readings awfully close) remain a good bet Saturday and Sunday -- temperature levels not seen here since late September.
Powerful south winds reached speeds of 43 mph in gusts at building-top levels on LaSalle Street Friday and 36 mph at Rockford, Lincolnwood, Burlington and north of the Wisconsin state line in Racine -- and have gusted to 30 mph at times overnight, mixing the air and preventing the usual nocturnal temperature drop. So Saturday's highs build from a higher starting temperature.
The air mass which dominates Midwest weather was so warm to the west of the city Friday it produced a second day of record-breaking highs in the Plains including 81 degrees at Valentine, Neb., 80 at Yankton and 77 at Rapid City -- both in South Dakota. Add to the air mass' inherent warmth the broad subsidence of air which is to occur Saturday beneath the nose of a powerful jet stream -- a process which helps heat the air as the sinking air is compressed in the higher pressures found near Earth's surface -- and there can be little question why weekend temperatures here are headed to levels 20 degrees above normal.
Warm spell to extend to 4 days -- not common this late in the season
With high temperatures exceeding 60 degrees predicted through Monday, this warm spell has only a comparative handful of peers over the term of Chicago weather records. Four days of temperatures 60 degrees or higher have occurred beyond Nov. 6 only once every six years on average. Records at the South Side site record only 13 comparable late-season warm spells in 81 years since 1928.
Dear Tom,
I have seen frost on garage rooftops at sunrise when temperature reports are 38 or 39 degrees. What gives?
Robert Wolfson
Dear Robert,
Frost forms when the shallow layer of air at the ground (or on any other surface such as a rooftop) cools below its saturation temperature (and below freezing) by contact with a cold surface that itself has cooled to a subfreezing temperature. Water vapor in the air condenses directly, in ice-crystal form, onto the cold surface: frost forms.
Under clear, calm nighttime conditions, surfaces like blades of grass (but it works for roofs, too) radiate a great deal of heat and their temperature drops sharply. The cold-air layer can be very shallow, often only a fraction of an inch. Air temperatures in National Weather Service reports are taken by temperature sensors a few feet above the ground and sheltered from radiational cooling.
The Chicago area appears headed for its mildest weekend since September--one which may include high temperatures within striking distance of 70-degrees. The eastbound mild air behind the predicted weekend warm-up sent temperatures Thursday soaring to near 80-degrees in the western Plains. In Denver, where up to 4 feet of snow fell in the mountains to the west of the Mile High City less than a week ago, the temperatures soared to 77-degrees with 81-degree readings at La Junta and Springfield--both in Colorado. Highs in nearby Nebraska included 81 at Sidney, 80 at Imperial and 78 at Chandron while Elkhart and Dodge City in Kansas topped out at 80.
The warming there was produced by air sinking from the mountains into the Plains where it was compressed and warmed as it descended into the higher pressures found at lower elevations. The process is commonly referred to as the Chinook effect.
As that mild air of Pacific origin continues eastward, it won't be quite as warm by the time it arrives in Chicago. But, it is likely to introduce a 15-degrees temperature increase by Saturday afternoon over the levels observed Thursday. Accompanying that warming will be an influx of Gulf moisture in the lowest several thousand feet of the atmosphere--enough to contribute to the "warmer" feel of the air, but, based on present indications from computer models, not deep enough to produce layer of the atmosphere to produce the kind of cloud cover which would block the sun and thwart warming. Arrival of more significant moisture supporting more extensive cloud cover appears the only means of sidetracking what seems on track to become one of the nicest weekends of the fall season--and that's not expected to happen at the moment.
Low clouds forming over western Illinois late Thursday evening were predicted to expand into the Chicago area Friday morning. But, powerful winds Friday are expected to mix down to the surface in the late morning and afternoon allowing clouds to break, some sun to emerge and temperatures to head toward 60-degrees. Gusts in excess of 30 mph appear a good bet once this happens---and, with gusty winds expected to continue Friday night and Saturday, overnight readings should be significantly milder than those of recent nights.
A fascinating weather scenario may unfold in the Caribbean and Gulf of Mexico in coming days and into next week. Minimal Hurricane Ida--with 75 m.p.h. top winds--went ashore in Nicaragua Thursday. The storm, downgraded to a tropical depression late Thursday, threatened torrential rains totaling 15 to 20 inches at higher elevations. But, computer models suggest the storm's northbound remnants are likely to sweep out over the bathtub warm waters of the Caribbean, allowing the system, in the absence of strong winds aloft to regenerate. The re-energized system is then likely to spread north into the Gulf of Mexico where it may threaten sections of the coast--- potentially including Florida with downpours and wind mid and late week.
Thursday's 100 percent cloud -free skies the sunniest in nearly 2 months
Thursday gorgeous, completely cloud-free skies produced Chicago's first 100 percent sunny day in the nearly two months since September 2 and 11.
Dear Tom,
What is the meaning of "northwest winds"? Wind coming from the northwest or blowing toward the northwest?
Ralph Bellendir
Dear Ralph,
By international convention, wind direction always refers to the direction from which the air is moving. The proper interpretation of, say, a northwest wind of 10 mph is that the wind is blowing from the northwest to the southeast at a speed of 10 mph.
While we're on the subject, here's an unusual bit of weather trivia: You'll never hear a reported wind speed of 11 mph. Never. Here's why: Wind speeds are always measured in knots (nautical miles per hour). That's the way it's done, worldwide, and then in the United States that value is converted to statute miles per hour. One knot is 1.1508 statute mph. A value of 9 knots converts to 10 mph and 10 knots becomes 12 mph after rounding to a whole number.
Shorter days and weaker, low angle sunlight make it harder to warm this time of year--but that doesn't keep mild temperatures from happening. The atmosphere just has to work harder to produce such "warmth"--by, for instance, generating stronger winds which blow from warmer regions into the Midwest before the incoming air can cool---or by minimizing cloud formation capable of blocking sunlight. It also doesn't hurt to sit beneath the nose of a pocket of powerful jet stream winds, where air sinks, compresses and warms on a broad scale---a setup predicted to fall into place this weekend. That warmth can occur this time of year was evident a year ago. The area was in the midst of a three day 70-degree spree. Last year's 71 degree high on this date was 18-degrees warmer than the 53 predicted Thursday.
Barring more extensive cloud development Saturday than is currently predicted, readings then could reach 70-degrees for the first time since Sept. 27. Late season 70-degree temperatures aren't common, but they have occurred beyond Nov. 5 an average of one year in three since records began at Midway Airport 80 years ago.
The coming warm-up---likely to produce the first set of back-to- back weekend 60s here since late September---may well be part of a three day spell of 60-degree-plus highs extending from Saturday through Monday. Three consecutive 60s have occurred here this late in the season in 44 percent of years on record.
Frigid arctic air remains trapped in northern North America where temperatures in recent days have dropped as low as 20-degrees below zero. In stark contrast, the tropics remain active. Tropical Storm Ida---with 65 mph winds and gusts of hurricane strength--formed Wednesday off the coast of Nicaragua. The system will lose strength as it punches into Central America on a northward trek. But, it's possible we've not heard the last of the system. It could emerge into the southern Gulf of Mexico off the Yucatan Peninsula in the next week where reorganization would occur.
Humidity surge this weekend will add to mild "feel"---over-development of clouds would thwart warming
Dew points, which reflect atmospheric moisture and have resided in the 30s in recent days, are to take off this weekend as Gulf moisture mixes with mild but comparatively dry Pacific air moving in from the west. They are to reach the 50s which will lead to a noticeably more "humid" feel to the air Saturday and Sunday just as temperatures surge. This should lead a mild feel to the air not experienced here since September.
Dear Tom,
We are approaching the 34th anniversary of the sinking of the Edmund Fitzgerald. How rare is it to have a storm of that magnitude on the Great Lakes?
Mike Long
Dear Mike,
The legendary storm of Nov. 9-10, 1975 had a central pressure of 28.95 inches when it crossed Lake Superior, equivalent to a Category 1 hurricane. At its peak, it had sustained winds of nearly 80 mph with gusts above 90 and produced giant waves 25-30 feet high.
Though stronger storms have battered the Great Lakes, this storm was certainly on the high end of severity scale. The term "Gales of November", popularized by mariners long before it was made famous by Gordon Lightfoot, refers to the peak of the Great Lakes' storm season, when late-fall storms fueled by clashing warm and cold air masses gain extra energy from the residual summer heat stored in the waters of the Great Lakes.
November is Chicago's fastest cooling month, a point driven home by Wednesday morning's chilly temperatures. Cloud cover and showers overnight prevented a repeat of the mid 20s recorded across a number of far western suburbs Tuesday morning. But, 30s were widespread and clouds and lingering sprinkles and light showers Wednesday will prevent daytime readings from rising out of the 40s ---the chilliest high temps here of the coming 7 days. Normal November highs tumble from 55-degrees on the first to 40-degrees on the 30th.
However, the month's tendency to cool hardly means all mild weather is behind us. A year ago, the Chicago area logged three consecutive 70-degree days (73, 71 and 71 on Nov. 3, 4 and 5.) And weather records reveal an average of one in three years has produced at least one additional 70-degree beyond this date and 93 percent of all years have added additional 60s. The 139-year average is four 60+degree highs past Nov. 4.
All signs point toward such a warm-up this weekend---a mild spell likely to extend into early next week. Late season warm-ups are extremely sensitive to cloud cover. Too much cloudiness or an outbreak of precipitation can take a serious toll on late year warm spells. So can a wind-shift off Lake Michigan. But, barring more cloudiness than is currently foreseen, the Chicago area could be in for a string of four 60-degree daytime highs from Friday afternoon through Monday. It would make the upcoming weekend this area's first since late September to host back to back 60s.
Computer models do indicate a weakness in the pressure field Saturday night into Sunday morning which has to be monitored. This may well allow a wind-shifting front to sag southward across the area. Such a development would permit southeast winds to take hold reaching lakeside counties after a trip over cool lake waters a portion of Sunday, lowering shoreline temperatures. But these same models take the front back north of the area and strengthen south winds Sunday afternoon and evening. Such a scenario would put 60s within reach of most of the Chicago area Sunday. And well organized south winds Monday and indications that most cloudiness is to remain to the west of the area until Monday night and Tuesday appear to favor more 60s Monday. Temperatures at such levels this time of the year are 15 to 20-degrees above normal.
Southwest sizzles in hottest late season air on record
Record warmth across the Southwest U.S. Tuesday produced a 96-degree high in Phoenix---the hottest temperature there ever so late in the season--- and a peak reading of 93 in Tucson.
Dear Tom,
I was able to see the stars clearly when I moved to Des Plaines 60 years ago, but now I miss seeing them at night. I understand gradually losing the ozone layer and the use of fossil fuels is to blame. Will I ever see the stars again?
Louise Koehler, Des Plaines
Dear Louise,
Triton College astronomer Dan Joyce shares your frustration and laments that "the grandeur of the nighttime sky" (as he refers to it) that was once a common spectacle has faded.
However, the decay of the atmosphere's ozone layer is not to blame because ozone only blocks the ultraviolet component of sunlight. Nor are fossil fuels at fault: the switch from coal to natural gas for heating has greatly reduced particulate pollution and our air is now clearer than ever.
The problem is light pollution. Metropolitan outdoor nighttime illumination is now so bright that it overwhelms our ability to discern the stars.
Temperatures are noticeably cooler Tuesday--but the abundance of
sunshine is likely to take at least a bit of the edge off the new surge
of chilly readings for sun-starved Chicagoans who are only three days
beyond the 3rd cloudiest, 9th wettest and 11th coolest October in 139
years of official observations here. The irony of the sun's return is
that it's happening in November--typically the city's second-cloudiest
month, also the month which cools the fastest. The new pattern
delivering the sun pulls a reinforcing shot of cool air into the area
Wednesday into Thursday--and has all but shut down the northward
spread of Gulf moisture responsible for rainfall here 22 of the past 32
days. Several brief showers--possibly coaxed into mixing with a few ice
pellets Wednesday morning as raindrops fall into very dry low-level air
producing evaporation and cooling--may occur Wednesday.
But
while 3.85 inches of rain has fallen in the past two weeks here, the
coming two weeks are likely to produce only 16 percent as much
precipitation--an amount closer to 0.63 inches according to an average
of the most recent rainfall projections off one of the National Weather
Service's key computer forecast models. It's a development which is
music to the ears of area farmers who continue in the midst of the
slowest, most vexing harvest season in recent memory. The weekly crop
progress report released Monday afternoon by USDA indicates that across
the 18 states responsible for 94 percent of this country's corn harvest
last season, only 25 percent of this year's corn crop has been
harvested compared to the five year average of 71 percent by this date.
Warmth (like this weekend's) still a good bet--though odds slide in November
With
strong warming predicted to lock in later this week, the Chicago area
appears in line to record its mildest weekend high temperatures in 6
weeks. The warm-up it to include a series of 60s from Friday through
next Monday. it's worth noting that a third of years since 1871 have
not only managed 60s this late in the season, but have gone on to
produce a 70-degree or warmer temperature in the November's opening
week. By November's final week, chances for a 70 here slip to near zero.
Dear Tom,
Why is it usually more cloudy in the autumn than in the summer?
Roger Hohman
Dear Roger,
The difference in the amount of heat provided by sunlight is the fundamental cause of seasonal variations in cloudiness.
In the warm season, the nearly overhead sun strongly heats the ground and overlying air. Currents of ascending warm air give rise to cumulus clouds that grow vertically into local cloud patches rather than spreading horizontally into widespread overcasts.
The opposite process prevails in the autumn and winter. Sunshine strikes the ground at a small angle and delivers little heat. The atmosphere grows colder, and the coldest layer is at ground level. Colder air under warmer is stable, and condensation and cloudiness tend to be horizontally stratified, resulting in widespread and long-lasting overcasts.
Much of the work week looks to be on the cool side with periods of cloudiness as minor weather disturbances move through. The upper-air flow pattern becomes more northwesterly, steering cooler air into the Midwest and holding milder air well to the south of the Ohio River. The jet stream will shift north by Friday with a weaker westerly flow aloft over Illinois, allowing milder air to ride southerly surface winds into northeast Illinois. While showers will be in the forecast off and on this week, expected rainfall should be on the light side. Thus runoff into rivers and streams will be primarily from the saturated soils, allowing for at least a little drying as the week goes on. Temperatures in the 60s and gusty winds over the coming weekend will also help to dry the soils, but again be tempered somewhat by the possibility of scattered showers.
Flood advisories
Flood advisories remain up for many rivers in states bordering on the Mississippi River from Louisiana all the way north to Illinois and Iowa. Most rivers in northeast Illinois and northwest Indiana are running close to bankfull, but the flood threat is farther to the south, the nearest being at LaSalle on the Illinois River.
Dear Tom,
It seems that 2009 has had an abundance of precipitation. Is this going to be a record wet year?
Chris Mall
Dear Chris,
Chicago is definitely having a wet 2009, but so far, this year is taking a back seat to 2008 which reigns as Chicago's all-time wettest year with a 50.86-inch precipitation total. Buoyed by September deluges that brought 13.63 inches of rain, 2008 marked the first time that the city's annual precipitation broke the 50-inch barrier, topping the old record of 49.35 inches established in 1983. At October's close precipitation at O'Hare Airport had officially reached 38.61 inches -- nearly 8 inches above normal -- but last year at the end of October the precipitation tally here was 43.28 inches -- 4.67 inches greater. Barring an incredibly wet close to 2009, last year's record should not be eclipsed.
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