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  • Tim McGill

Big Model Difference In Snowfall Forecast

Coldest Air Of Season So Far Is Coming


We've been spared any real brutal blasts of Arctic air so far this winter. We have yet to dip below zero. We have yet to have a day with a high temperature in the teens. The coldest day so far this winter was Christmas day. We had a low that morning of 8° and a high of 22°. December ended up 5.1° above average overall and January is now running just under 7° above average.


Cold air is coming though. It will be with us briefly but the timing, right after a warm up today, will mean a shock to our system.


First the good news. Today's highs with the help of some sunshine should soar to near 40°. Gusty winds will make it feel colder though.



One dramatic drop comes tonight after Arctic air sweeps in on gusty northwest winds following the passage of a cold front. That front might squeeze out a few flurries or a light snow shower tonight. The front means we fall from near 40° today into the teens for tomorrow morning's lows. Another fairly dramatic drop comes Friday night. We fall from the middle 20s for highs Friday down into the single digits by early Saturday morning. We will go from the warmest day of the week today to the coldest morning of the season so far by Saturday morning.


The wind will make it feel even colder. Despite highs nearly 10° above average today, it will feel like the teens and 20s with winds gusting to near 30 mph. Wind chills dip into the single digits tonight into Friday then fall below zero by Saturday morning.



The GFS model shows lows Saturday morning plunging to near zero in northwest Illinois with single digits common here. Lows in the city should drop to about 10° to 15°.



The dramatic drop that is coming is best visualized with the GFS model temperature anomaly forecast. It has northern Illinois around 10° above average today but nearly 10° to 20° below average by Saturday morning. It will feel nearly 40° colder Saturday morning compared to this afternoon.


GFS temperature anomaly forecasts for Thursday afternoon (left image) and Saturday morning (right image) courtesy of ClimateReanalyzer.org.




A Couple Snow Systems To Watch


O'Hare saw its seventh straight day with snowfall yesterday. During that stretch 3.2" of snow fell in total. So far this winter there has been 7.9" of snow compared to an average to date of 15" for the season.


The GFS model cloud cover and precipitation meteogram has some light to moderate snowfall coming Saturday night into Sunday. It hints at another system with even lighter snowfall for the middle of next week arriving late Wednesday.


The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. It suggests an inch to a bit over 2" for the weekend system. Next Wednesday's system squeezes out just a few tenths of an inch of new snow.







No Model Consensus Yet


The GFS model forecast has most of our weekend snow coming late Saturday into Sunday. It suggests about one to nearly three inches of snow could be coming.

The European model is the model of choice for snow lovers. This model squeezes out just a few tenths to an inch of snow with Sunday's system but then piles on nearly a foot of additional snow with another system Monday into early Tuesday morning. The GFS model keeps that second system well south of us. A tricky forecast considering the lack of consensus. Stay tuned as the models refine and update closer to the event.


ECMWF Model Total Snowfall Accumulation Forecast Through Tuesday Morning (Pivotal Weather)



Temperatures Trending Milder?


The long range temperature probability forecasts are hinting at a milder pattern developing for the start of February. The 6-10 day temperature probability forecast has the Chicago area outlooked for about average temperatures overall from January 26th through January 30th. The longer range 8-14 day forecast favors us for above average temperatures overall for the period from January 28th through February 3rd. That is consistent with the experimental multi-model ensemble temperature anomaly forecast discussed below.





The experimental multi-model ensemble has us outlooked slightly below average for the week ending on February 5th. It bumps us up a bit above average for the following week of February ending on the 12th.



The experimental multi-model ensemble temperature anomaly forecast for next month keeps the mild pattern we saw for the first two months of winter coming for February too. The only part of the country with below average temperatures on the map is a small portion of Washington and Idaho.


The precipitation probability forecast for February has the Midwest, including Chicago, and most of the northern half of the country outlooked for above average precipitation overall for next month. The southern tier of the US is outlooked for below average precipitation which is consistent with a La Nina pattern.





More Active For Start Of February?


The long range precipitation probability forecasts start out favoring us for below average precipitation then flipping in early February to above. The 6-10 day forecast from January 26th through January 30th has us outlooked for below average precipitation overall. We are on the western fringe of a large area outlooked for below average precipitation that stretches from here through the eastern Great Lakes to the New England area. The 8-14 day forecast has us outlooked for above average precipitation from January 28th through the February 3rd. This would be consistent with the experimental multi-model ensemble precipitation probability forecast for February discussed above.







Here is my 7 day forecast:


Today: Mostly sunny, blustery (gusts to 30 mph) High: 39


Friday: Partly to mostly sunny Low: 16 High: 24


Saturday: Partly to mostly cloudy (light snow overnight) Low: 8 High: 27


Sunday: Cloudy, light snow at times Low: 24 High: 34


Monday: Mostly cloudy, chance of light snow Low: 25 High: 34

Tuesday: Partly to mostly cloudy Low: 23 High: 32


Wednesday: Partly to mostly sunny Low: 22 High: 33


#ilwx

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