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Chicagoans shivered through a second day of arctic air with Tuesday producing a high of just 32-deg—the coldest day of the month. Even colder were the wind chills which ranged from 10 to 22-deg all day. The chill followed the coldest morning lows: 18 at O’Hare and 19 at Midway with 11-deg lows west of the city—in 3 weeks.
It’s the coldest spell of weather in 3 weeks and represents only the 2nd December 2023 day to produce a BELOW NORMAL average temp. The cold spell is particularly jarring since it’s come in a month with only 2 days BELOW NORMAL.
Yet even with today’s chill factored in, December 2023 is running 5.7-deg ABOVE NORMAL and 4.3-deg warmer than the opening 19 days of the month a year ago.
The good news is MILDER PACIFIC AIR IS ON THE MOVE and temps Wednesday afternoon are expected to be nearly 10-deg warmer than today. Daytime average temps return to ABOVE NORMAL STATUS Wednesday and current modeling establishes an ABOVE NORMAL OVERALL TEMP PATTERN through the next two weeks.
In fact, by the weekend, temps will be flirting with 50-deg highs and in the low 50s Christmas Eve Day (Sunday) and Christmas Day itself. This nixes any chance for a White Christmas. Christmas Day is likely to see rain—and there could even be an isolated t-storm. If this actually happens, it would be the first Christmas on the books dating all the way back to 1871 in which a Dec 25th produced a t-storm. Thunder prospects are hardly certain—but with low 50-deg dewpoint and a vigorous winter storm system sweeping toward Chicago and sending a moist flow of moisture northward into the Midwest by then, it wouldn’t be impossible to see such an atmosphere popping a t-storm. One thing IS for sure—SNOW is NOT in the offing.
A check of past Christmases shows only 8 of the 23 Christmases since 2000—that’s just 35% of Christmases—- have met the criteria for A WHITE CHRISTMAS DESGINATION—namely, Dec 25’s which open with an inch or more of snow on the ground. And over the 139 years dating back to the beginning of the city’s official snow record which started in 1884, only 56 of those 139 Christmases—or 40% of them—have opened with an inch or more of snow on the ground. That means climatological odds actually favor Christmases WITHOUT a cover of snow.
Some rain is expected to precede the wet Christmas winter storm system—and that’s to arrive with a “lead system” due to sweep the area Thursday night into Friday.
ALSO IN THE CARDS—the ASTRONOMICAL START TO THE WINTER 2023 SEASON. That happens at 9:27 pm CST Thursday evening—at the moment of the WINTER SOLSTICE. That’s the moment the sun’s most direct rays are falling as far south on the planet (in the southern hemisphere) as at any time of the year.
A solar noon Thursday, the sun will appear only 25-deg above the horizon versus 72-deg above the horizon on June 21st. The higher angle at which sunlight arrives when the sun is so low in the sky means less energy arrives here with the sunlight. Thursday’s sunlight will deliver less than half the energy of sunlight in summer. That plus the usual build-up of a snow pack is key to the chilly temps which arrived with winter.
Fortunately, not only is an El NIno, which seems likely to be one of the top 5 strongest El Ninos on the books leading to more frequent surges of mild Pacific air into the Midwest, but only 16.9% of the Lower 48 has a cover of snow compared to 43.6% on this date a year ago. That’s just 38% of the area covered by snow at this time ion 2022. This more limited snowpack is contributing to the warmer than normal temp regime which has dominated the month up to the arrival of the current arctic air.
HERE IS MY LATEST TUESDAY CHICAGO METRO FORECAST (12/19/2023)
TONIGHT: Partly cloudy and, while chilly, NOT QUITE A COLD as last night. Low 23 at O’Hare and upper teens inland—but steady or slowly rising readings late.
WEDNESDAY: Partly sunny, noticeably milder in the afternoon. High 41-deg—a reading nearly 10-deg warmer than today.
WEDNESDAY NIGHT and THURSDAY: Extensive cloudiness and milder. There may be some sprinkles later Thursday. Low Wed night 30. High Thursday 41.
FRIDAY: Rainy spells from a thick overcast. Mild for the season. High 48.
SATURDAY AND SUNDAY: More cloudy than not, mild and hazy. Some light rain or sprinkles possible from time to time. High Saturday 48. Sunday’s high 52.
MONDAY (Christmas Day): Rainy, hazy and unseasonably mild. Isolated thunder can’t be ruled out. High 52.
TUESDAY: The overcast lingers, mild. Some light rain or sprinkles at times. High 49.
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