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  • Tim McGill

Snow Followed By Possibly Historic Cold

So Far, Mostly So Good

Most of this winter has been fairly quiet as Chicago winters go. We did pick up quite a bit of snow in the last week or so. In just one week we saw half of a typical winter's snowfall. An average winter (December-February) produces about 27.1". We saw 16.8" between January 25th through the 31st alone. It did help that the biggest chunk of that (10.8") fell mostly overnight Saturday into Sunday morning. That is probably the period when snow could fall with the least amount of impact.

The Accumulated Winter Season Severity Index (AWSSI) keeps a running tally on just how extreme a winter a certain location is having. It is more commonly known as the "misery index". We have jumped just a bit over the past week or so towards a higher level of misery but remain firmly in the middle of the "mild" category or the least miserable of all categories.

Only four locations in the entire country are considered to be worse than average so far this winter. They include Trinidad and Grand Junction, Colorado and Madison, Wisconsin. Those three towns are having a "severe" winter. Just one town, Payson, Arizona, is having an "extreme" winter. More east coast towns may move into a worse winter category after the effects of this week's northeaster is included in their index.

Tracking Temperatures

The first day of February continued the trend we have seen in both December and January. February 1st was 4° above average. December ended up 5.1° above average and January was even milder, finishing 5.4° above average. Our relatively warm winter pattern will continue through Thursday before a dramatic drop comes just in time for Friday and the weekend.

Today's highs should top out right around average in the lower 30s.

We warm up through Thursday when highs approach 40°. An Artic front comes through Thursday night that could cause a "flash freeze". Temperatures may fall so suddenly that any moisture on untreated roads will freeze within a few minutes. We could fall from near 40° Thursday to wind chills ranging from -15° to -30° at least by Sunday morning. In other words, it will feel almost like a drop of 70° between Thursday and early Sunday.

The latest GFS model model run still has lows plummeting to 15° to 25° below zero Sunday morning. Wind chills could be as cold as -30° to -50°. It has been consistently calling for the arrival of Arctic air by Friday. It now appears likely we will have a bitter blast of Arctic air here later this week although the actual forecast numbers may change. A record that goes back 146 years may fall this weekend. The record low for Sunday is -10°. If the GFS forecast verifies, we would shatter that record.

The temperature anomaly forecast for Sunday morning shows the extent of the Artic air invasion. The bitter blast would sweep well into the south. The Texas panhandle would be close to 20° below average. Northern Illinois would be 25° to 40° below average.

More Sticking Snow

The GFS model cloud cover and precipitation meteogram has some rain arriving by late Thursday that would mix with and change to snow by early Friday. There could be a period of freezing rain south of the city during that time. There could be a few inches with this next round of snow. It will be followed by two brief periods of lighter snow on Sunday and then next Monday.

The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. Thursday's snowfall range is anywhere between a bit more than a dusting to nearly 7" of snow. Those numbers have gone up in the latest run of the model. The other smaller bumps represent lighter snowfall amounts possible late Saturday and Monday.

Coating Of New Snow Coming

The GFS model squeezes out two to three inches of new snow here late Thursday into early Friday. Heavier amounts that could approach 6" are forecast for our far northwestern suburbs.

The European model lays down even more snow with the next system. It spits out around 3" south of the city, around 4" in the city and up to nearly 7" northwest of Chicago.

Most Of Country Covered In Blue

The latest long range temperature probability forecasts have most of the country favored for below average temperatures overall through the middle of the month. Some of the darkest shades of blue which indicate the higher probabilities are centered near or over Chicago. The latest 6-10 day temperature probability forecast has the Chicago area outlooked for below average temperatures overall from February 7th through February 11th. The longer range 8-14 day forecast continues to keep us outlooked for below average temperatures overall from February 9th through February 15th. Once this cold pattern kicks in over the weekend it could hang around.

The even longer range Subseasonal Experiment (SubX) forecast seems to suggest February will stay frigid (overall) through nearly the end of the month. The forecasts for both the week ending February 19th and the week ending February 26th have us favored for below average temperatures overall.

More Moist By Middle Of Month

The trend in the long range precipitation probability forecasts points towards a more active pattern for the middle of February. The 6-10 day forecast favors us for around average precipitation overall from February 7th through February 11th but the 8-14 day forecast has us outlooked for a return to about average precipitation overall from February 9th through February 15th.

Here is my 7 day forecast:

Today: Partly to mostly cloudy High: 32

Wednesday: Partly to mostly sunny Low: 15 High: 34

Thursday: Rain or wintry mix changing to snow Low: 27 High: 39

Friday: Partly to mostly cloudy, patchy blowing/drifting snow Low: 10 High: 19

Saturday: Mostly cloudy, light snow possible Low: 2 High: 14

Sunday: Mostly cloudy, very cold Low: -10 High: 7

Monday: Partly to mostly sunny Low: -8 High: 10



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