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  • Tim McGill

First Surge Of Arctic Air Arrives Tonight

50s Then Dramatic Drop


Winter seems to have been put on hold lately. Today will be the fifth day in a row with highs at least in the 40s. This month is now running over 6° above average. Our highs today are typical for late March or early April. Gusty southwest winds will push our highs into the lower 50s. The winds could gust over 50 mph. The National Weather Service has issued a wind advisory through 4 am Thursday morning.

An Arctic front will sweep through late today setting us up for a dramatic drop in temperatures. We'll fall from the 50s today to the teens tomorrow morning. After today there are no 40s in sight through the middle of next week at least.


The combination of gusty winds and cold temperatures will make it feel like near or below zero starting early tomorrow morning, through Christmas Eve and into Christmas morning. The worst wind chills will be early Christmas day when it will feel like -5° to nearly -15°. By tomorrow morning it will feel almost 60° colder compared to this afternoon.





More Active Pattern Coming


It has been a quiet month so far in terms of precipitation. We've had five days with just a trace of snow and two days with rainfall this month. We are nearly six inches below average for snowfall to this point.


The GFS model has three systems to watch with at least some precipitation over the next ten days. Some rain is expected mainly later today and will change to light snow overnight into early tomorrow morning. Little or no accumulation expected with this first system. The second system could bring us some light snowfall late Sunday into Monday with at least some minor accumulation. The third system could make things messy for the middle of next week with a mix of rain, freezing rain, sleet and snow possible.


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


Between the brief changeover to snow tonight and an occasional snow shower or a few flurries from time to time Christmas Eve to early Christmas morning, there could be some spots that get a light coating of snow. It won't be enough for an official White Christmas but it will be reminder that winter has finally arrived. There will also be some lake effect snow in northern Indiana with as much as one to four inches possible there. The potential for some sticking snow increases for late Sunday into Monday. Rain may mix with and change over to snow. The GFS model tries to squeeze out a couple of inches.





White Christmas For North Central Indiana


The latest GFS model doesn't show any accumulating snow for northern Illinois between now and Christmas afternoon. There is hope for a White Christmas though in north central Indiana. Portions of Porter county and LaPorte county could end up with as much as two to three inches of some fluffy snow between tomorrow and Christmas day.


This is the snowfall accumulation forecast through Christmas afternoon.

The European model accumulated snowfall forecast is similar for the same period. The only difference is it suggests a dusting for some spots along the lakeshore in Illinois. Notice the heavy snowfall expected for portions of Minnesota and northern Wisconsin. There are blizzard and winter storm warnings posted for heavy snow accompanied by strong winds there.




Christmas Through The Years


This will be a cold Christmas compared to average. Average highs for December 25th are around 32°. We will end up about 10° below average on Friday. That would make it the 34th Christmas out of 145 with a high in the 20s.


We aren't expecting any significant snowfall on Christmas day. That would make this Christmas the 63rd of 133 with no snowfall. 41% of our Christmases have been white (1 inch of snow or more on the ground). 39% of Christmases see measurable snow with the snowiest Christmas back in 1950 when 5.1" fell.



Looking Longer Range


The longer range temperature probabilities have us favored for about average temperatures from the end of 2020 through the first five days of 2021. The 6-10 day temperature probability forecast has us about average temperatures overall from December 28th through January 1st. The longer range 8-14 day forecast also has us outlooked for near normal temperatures overall too from December 30th through January 5th. The signal isn't as strong though with the probabilities dropping a bit compared to prior forecasts.





Near Or Above Average Precipitation


The longer range precipitation forecasts both favor us for about or just above average precipitation overall. The 6-10 day forecast from December 28th through January 1st has us outlooked for above average precipitation. The 8-14 day forecast from December 30th through January 5th also has us outlooked for between near normal to above average precipitation. Like the longer range temperature probabilities, the signal isn't as strong as prior forecasts with the lighter shades of green over northern Illinois representing the lower end of the probabilities range.







Here is my 7 day forecast:


Today: Mostly cloudy, windy, rain mainly late High: 52


Thursday: Partly/mostly cloudy, few flurries, blustery High: 23 early but falling into the teens

Christmas: Partly to mostly sunny & cold Low: 7 High: 22

Saturday: Partly to mostly sunny Low: 18 High: 36


Sunday: Mostly cloudy, light rain/snow possible late Low: 27 High: 40


Monday: Partly to mostly sunny Low: 27 High: 32


Tuesday: Partly to mostly sunny Low: 28 High: 29


#ilwx

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