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Temps to build toward unseasonably mild 50s Sunday and Monday; Christmas rain likely
WGN WEATHER HEADLINES
IT WAS DECEMBER’S COLDEST MORNING TO DATE ACROSS THE CHICAGO AREA
With low temps of 18 at O’Hare and 19 at Midway and even colder in areas surrounding, the Winter Solstice, the astronomical start to the winter season, occurs in the northern hemisphere this Thursday, December 21 at 9:27 PM CST Chicago time — our shortest day of the year
- No morning’s been colder this month than the readings which greeted us Tuesday morning. In fact, this morning’s upper teen low temps were the coldest to occur in the city since a 14-degree minimum temp the morning of November 28th.
- But temps are to bounce back in coming days, resuming the ABOVE NORMAL TEMP TREND which has dominated the month. Until Monday, EVERY DECEMBER 2023 DAY HAS POSTED A TEMP SURPLUS.
CHICAGO AND THE NORTHERN HEMISPHERE’S SHORTEST DAY OF THE YEAR TAKES PLACE THURSDAY
Chicagoans will see only 9.1 hours of daylight (548 mins) versus the 15.2 hours (which occurs when summer begins (914 mins) astronomically June 21 — that means Thursday will see 6.1 hours less daylight than on June 21st
Some interesting notes on this Thursday’s astronomical start of the winter season:
- The WINTER SOLSTICE, IS the precise moment the winter season begins astronomically is 9:27pm CST Thursday evening, December 21st. It’s also the moment of the year the sun’s most direct rays fall as far south on Earth as at any other time of the year.
- The sun, observed from Chicago, will trek as far south across the sky Thursday — sitting just 25 degrees above the horizon at solar noon Thursday versus 72 degrees above the horizon on June 21st as astronomical summer begins.
- Sunlight which arrives less directly when the sun is that low in the sky arrives at a the greatest angle of any day of the year — and sunlight coming in at an oblique angle like that delivers less energy. Sunlight Thursday will deliver only 45% of the energy of June sunlight. This, plus factors like the extent of reflective snow cover and of cloudiness (which tends to be higher here in Chicago in December versus June) is the reason it turns colder in the winter season.
- The period of daylight Thursday will be just 38% of the 24 hour period versus 63% of the 24 hour day in June.
- Days will begin to lengthen very shortly beyond Thursday — increasing by less than a second the Dec 22 then by 4 seconds on the 23rd, 8 seconds on the 24th and 14 seconds on the 25th.
- Daylight will increase to greater than 10 hours January 31st to greater than 11 hours in length February 24 and to over 12 hours in length by March 13th.
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Near the time of the lowest overnight temps Tuesday morning -
This shows where Tue morning temps were BELOW and ABOVE NORMAL -
Here’s a graphic which lays out where the sun’s most direct rays fall at the time of the Winter Solstice — which takes place Thursday at 9:27pm CST December 21, 2023 -
NASA depiction of the summer versus the winter solstices
LOOKS LIKE A “WET” RATHER THAN A “WHITE CHRISTMAS” THIS YEAR
A windy wet storm with temps very possibly topping 50 degrees is on the way for Chicago
- We have 139 years of official snow data dating back to the 1884-85 winter snow season here. Over those 139 years, 83 have had at least a “trace” of snow on the ground in Chicago — that’s 60% of winters. Of those 83 Christmases, only 56 have had an inch of more and have qualified as “White Christmases” thats 40% of them.
- But since 2000, only 35% of Christmases have had 1″ or more snow on the ground. This included LAST CHRISTMAS when 1″ of snow was on the ground Dec 25th. That means WHITE CHRISTMAS frequency is down 5% in the past 23 years. Could that be the product of a reduction in snowfall related to our warming climate? Sure looks like that’s plausible.
CLICK TO ENLARGE
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