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  • Tim McGill

Is Real Chicago Winter Weather Around The Corner?

Forecast Key Is Above My Head & Yours Too

I've described this as a wimpy winter so far. As I noted on Monday, the Accumulated Winter Season Severity Index or AWSSI keeps track of the relative severity of our winter so far. It is firmly in the "mild" category or the least miserable of all the categories. The categories from least miserable to worst are mild, moderate, average, severe and extreme. Still no signs of this changing for at least the next week or so. Those of you who miss the more brutal Chicago brand of winter have some hope though as we look longer range.

We live in the lowest layer of the atmosphere called the troposphere where most weather takes place. Just above this layer lies the stratosphere and what is happening there now could have a big impact on what will be happening down here fairly soon.

Temperatures have recently risen rapidly in the stratosphere. This event is referred to as a "sudden stratospheric warming" or SSW for short. This tends to disrupt the polar vortex, a large low pressure system that contains the core of the coldest air over the Earth's poles.

Remember the winter of 2013-1014 when Chicago earned the nickname "Chiberia"? That was a winter that saw frequent frigid portions of the polar vortex dislodge and descend upon us. The coldest air tends to stay trapped over the North Pole when the polar vortex is strong but when it weakens, chunks of bitter cold air can slip south. The SSW occurring nearly 20 miles above the pole may cause the polar vortex to wobble and send colder air towards us anywhere from about two weeks to a month from now. While the confidence is fairly high for some colder air to visit there is no guarantee this will translate into a surge of snowfall. Cold is critical for snow of course so this scenario gives us at least a fighting chance to erase some of this winter's snowfall deficit.

In the meantime it is business as usual in Chicago with another grey day expected. Expect some morning fog and a few flurries today. Our highs should be in the middle 30s to make this the 12 straight day with temperatures above average. The average high for this date is 31°. January is now running 5.7° above average.

Signs Of Snow Next Week

So far this winter we have seen 4.5" of snow which is less than half of normal to date. We should have 9.8" by now. The GFS model precipitation meteogram hints at a more active pattern for snow developing next week. It hints at a little lake effect snow on Saturday then several chances for at least light snow next week.

The grand total from the GFS model for snowfall accumulation over the next two weeks is about two to three inches for most of us. Heavier lake effect snow is shown on the other side of Lake Michigan.

The European model is calling for just a bit over an inch over the next ten days. So it appears neither model is suggesting big storms but at least they are offering some hope for snow lovers.

Back To About Average?

There could be a change in our relatively mild pattern coming later this month. The longer range temperature probabilities forecasts no longer have us outlooked for above average temperatures overall. The long range models now favor us for about average temperatures just past the middle of January. The 6-10 day temperature probability forecast has Chicago and areas north and west of here outlooked for near normal temperatures overall from January 11th through January 15th. A similar pattern is shown for the longer range 8-14 day forecast. It continues to favor us for about average temperatures overall during the period from January 13th through January 19th too.

At Or Above Average Precipitation

The longer range precipitation probabilities forecasts has us outlooked for either above average or around average precipitation during the middle of the month. The 6-10 day forecast from January 11th through January 15th has us outlooked for below average precipitation. The 8-14 day forecast has us near normal in northern Illinois for precipitation from January 13th through the 19th.

Looking Even Longer Range

The experimental multi-model ensemble temperature probability forecast keeps the relatively mild pattern coming through the end of the month. Not only is the Midwest favored for above average temperatures overall from January 16th through the 29th but most of the country is outlooked to be above average (lower left image). Not much of a signal regarding the precipitation outlook for the same period (lower right image). The forecast calls for equal chances of being above or below average with precipitation.

A Look Back At Last Year

Did 2020 feel warm to you? It should have. It was the 5th warmest year on record for Chicago with an average temperature of 53.3°. Snowfall was fairly scarce last year too. We ended up with 28" total which is more than 8" below average for the year.

Here is my 7 day forecast:

Today: Fog & a few flurries early, mostly cloudy High: 37

Thursday: A.M. patchy fog, cloudy skies, flurries possible Low: 28 High: 38

Friday: Mostly cloudy Low: 29 High: 37

Saturday: Partly to mostly cloudy, flurries near the lakefront Low: 25 High: 36

Sunday: Partly to mostly cloudy Low: 24 High: 34

Monday: Partly to mostly sunny Low: 23 High: 32

Tuesday: Partly to mostly sunny Low: 25 High: 33



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