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  • Tim McGill

It's Beginning To Look A Lot Like Winter

Typical Temperatures Today


Not one but two systems this week will bring us a wintry mix of precipitation. The first arrives this afternoon and continues overnight and well into Wednesday and the second comes Thursday night and lasts into at least New Year's Day.


Two to five inches of snow is expected for most areas (including Chicago) with the higher end of that range the further north and west you go. For McHenry and DeKalb counties and areas further north and west from there, up to four to eight inches of snow is possible. There could be a tenth of an inch of ice or a bit more with the messy mix that develops overnight. Another one to three inches of snow could fall north and west of the city with the second system later in the week. More on the snowfall numbers below.


Tricky temperatures that hover near the freezing mark today into early tomorrow means our first system will produce a variety of precipitation types.


Today's highs will be in the lower 30 with southerly winds making it feel like the 20s. Tonight's temperatures won't dip too much from today's highs so this should end up being another above average day overall. Only five days this month have been below average. December is now running a bit over 5° above average.





Snow Then Messy Mix


Today's system starts off with snow spreading from west to east across the area this afternoon. Snow will change to a mix of freezing rain and sleet overnight. The messy mix will change to rain early on Wednesday. Rain tomorrow will change to light snow before it ends later in the day.


A winter weather advisory is in effect for most areas including the city from 3 pm today through 9 am Wednesday with a winter storm warning for heavier snowfall amounts in our far northwester suburbs and the northwest corner of Illinois



We get a break between systems Wednesday night through Thursday before the next one arrives on Friday.

The GFS model's precipitation meteogram shows the timing of both systems.





Break Out The Shovels


The GFS model continues to favor areas northwest of the city for the heaviest snowfall totals with our first system.


It is suggesting an inch or two in the city and through northern Indiana with up to four or five inches or more in far northern and northwestern suburbs.


I ran out the snowfall accumulation forecast into Saturday morning to include the second system's snowfall. This system adds another one to three inches of snow to areas mainly north and west of the city.



The European model accumulated snowfall forecast is similar for the first system with an inch or two in the city but heavier amounts in far northwestern suburbs.


ECMWF Snowfall Accumulation Forecast Through Wednesday (Pivotal Weather)

The European model adds an additional one to three inches with the second system too but delays that snowfall a bit compared to the GFS model. It has it arriving more towards Friday night and lingering longer into Saturday but the overall numbers for total snowfall with both systems looks similar to the GFS solution.

ECMWF Snowfall Accumulation Forecast Through Saturday (Pivotal Weather)

The second system's snowfall could change based on how the first system verifies. I want to stress that both systems are complicated and their timing and tracks will be critical in determining precipitation amounts and types.




"Mild" Start To New Year


The longer range temperature probabilities have us favored for above average temperatures overall for the start of 2021. The 6-10 day temperature probability forecast has the most of the country outlooked for average temperatures overall from January 3rd through January 7th. The longer range 8-14 day forecast continues to favor us for above average temperatures overall during the period from January 5th through January 11th.





"Mild" Stretch Well Into January?


December will end up as the 10th month this year to have temperatures overall above average. The experimental multi-model ensemble temperature anomaly forecast suggests January may also end up above average too. The forecasts for both the week ending on January 15th and the week ending on January 22nd both have us outlooked for above average temperatures overall.





More Active Pattern?


The two systems this week might mark a change towards a more active pattern as we head into the start of the new year. The longer range precipitation forecasts both favor us for above average precipitation overall. The 6-10 day forecast from January 3rd through January 7th has us outlooked for above average precipitation. The 8-14 day forecast from January 5th through the 11th also has us outlooked for above average precipitation overall too with slightly higher probabilities. The precipitation that does fall during this period could be more rain than snow considering the temperature probability forecast has a fairly strong signal for above average temperatures.








Here is my 7 day forecast:


Winter Weather Advisory For Most Areas From 3 PM Today Until 9 AM Wednesday

Winter Storm Warning For Northwestern Suburbs From 3 PM Today Until 9 AM Wednesday


Today: Mostly cloudy, light snow developing in the afternoon High: 33


Wednesday: Rain early, mix of rain/snow possible late, windy Low: 30 High: 39


Thursday: Partly to mostly cloudy Low: 27 High: 33

New Year's Day: Light mix early, rain and snow in the afternoon Low: 28 High: 40

Saturday: Partly to mostly sunny Low: 29 High: 35


Sunday: Partly to mostly sunny Low: 23 High: 36


Monday: Partly to mostly cloudy Low: 27 High: 38


#ilwx

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