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  • Tim McGill

Putting A Dent In Snowfall Deficit

Rain First Then Snow

Some snow is on the way but a relatively warm Thursday means we will see some rain first. Highs today should climb to nearly 40°. Today will be the 20th straight day with temperatures above average. January is now running just under 7° above average. The average high for this date is 31°. So far this winter is running about 6° above average.

Highs today will range from the upper 30s north and west of the city to as warm as the lower 40s south and east.

After a relatively warm week temperatures finally fall on Friday into the middle 30s. Temperatures continue to tumble to near 30° for a high by Monday. After this afternoon it will be cold enough to support several chances of light snow over the next six days. More on that below.

Colder air is definitely coming but we only fall to around or just a bit below average next week. Previous blog posts have warned about a possible upcoming shift to a much colder pattern. A "sudden stratospheric warming" could jostle the polar vortex and send some lobes of Arctic air our way. That threat is still with us and looking really long range it shows up on the temperature anomaly forecast. Look at the contrast between today's temperature anomalies (lower left) and the forecast for a week from this Saturday (lower right). Most of the Midwest today will be between 10° to 20° above average today. By the morning of January 23rd most of the Midwest is 10° to 20° below average.

Several Snow Chances

Our snowfall deficit for this winter is now at 7.8". We have seen 4.7" of snow so far at O'Hare and on average we should have 12.5" by now. The GFS model cloud cover and precipitation meteogram shows at least six chances for some light snow over the next ten days.

Most of the accumulating snowfall in our forecast will fall tonight and during the day on Friday. The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. The range of forecasts for snowfall late today into Friday is anywhere from a dusting to nearly two inches. I boxed the other periods that show bumps by the models representing additional possible minor accumulations

The Grand Totals

The GFS model forecast spits out a grand total of about 1" to 4" for most of us from late today through Monday morning. The lighter amounts (around an inch) are seen along the lakeshore with the heavier amounts northwest of the city and in northern Indiana.

The European model is calling for similar snowfall overall during the same period. It spits out about 1.5" to 4" in total. I'm expecting about an inch or a bit less in the city and southward but 2 to 4 inches northwest of the city and in north central Indiana when it is all added up through Monday morning. Our first round of snowfall late today into Friday will probably total about a half inch to an inch in the city and southward to 2" or a bit more northwest of the city and in northern Indiana.

Hints Of Harsher Winter Weather

I want to share two more long range forecast graphics that support a turn towards a more harsh winter pattern could be coming in a few weeks. Looking very long range at the GFS model temperature forecast for the morning of January 26th shows some sub-zero readings in our far northwestern suburbs. These numbers will no doubt fluctuate between now and then but this model continues to hint at a much colder brand of air may be coming.

The long range GFS snowfall accumulation forecast brings snowfall totals up to over a half a foot of snow in total between now and just over two weeks from now. That means an additional 3 to 5 inches of snow could be coming beyond this weekend. This is something to keep an eye on too. These snowfall projections this far out can notoriously bust but if we see consistent forecasts like this, it might be a signal of a more active pattern to come.

Signal Of Colder Pattern Coming

This month has been relatively mild but it might not end that way. Today's longer range forecasts continues to hint at a possible colder pattern coming by the end of the month. The 6-10 day temperature probability forecast has Chicago outlooked for above average temperatures overall from January 19th through January 23rd. The longer range 8-14 day forecast has most of the country from here westward outlooked for below average temperatures overall during the period from January 21st through January 27th. This expanding area of blue could mark the turn towards a period of more invasions of Arctic air.

More Moisture Across The Country

Our long range precipitation probability forecasts has a lot of green on them. Both show the vast majority of the country is favored for above average precipitation overall for the last part of January. The 6-10 day forecast from January 19th through January 23rd has us outlooked for below average precipitation overall. The 8-14 day forecast has even more of the country outlooked for above average precipitation from January 22st through the 27th. If a colder pattern does settle in to coincide with this shift towards a more active precipitation pattern it would mean more snow is coming too.

Here is my 7 day forecast:

Today: Cloudy, light rain/snow develops pm High: 39

Friday: Light snow early then light rain/snow showers pm Low: 31 High: 35

Saturday: Mostly cloudy, light snow showers Low: 26 High: 38

Sunday: Mostly cloudy, light snow showers Low: 27 High: 32

Monday: Mostly cloudy, light snow showers Low: 22 High: 31

Tuesday: Mostly cloudy Low: 25 High: 35

Wednesday: Mostly cloudy Low: 23 High: 36



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