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  • Tim McGill

Snow Definitely Coming But Question Is How Much?

Brief Brush With Artic Air


We can't complain too much about being cold this winter. Yesterday was the 27th straight day with above average temperatures. That streak may finally come to an end today. We will be on the southern fringe of some frigid air today and tonight. The main push of Arctic air is just to our north.


Highs today will range from the teens over the heavier snowpack northwest of the city to the middle 20s south and south east of Chicago. This will be close to the coldest highs we have seen so far this winter. The coldest high was 22° back on Christmas day.



This will be a quick shot of bitter cold air though. Our highs bounce back to near 30° Saturday and we should have highs at least 30° or above then through Thursday.



The combination of cold temperatures and a brisk breeze will make it feel like near zero with the wind chill early today and at best only single digit wind chills this afternoon. Wind chills will drop to near or below zero by early Saturday morning.



Tonight could be the coldest night of winter so far. The GFS model shows lows Saturday morning plunging to near or just below zero in northwest Illinois with single digits common here. Lows in the city should drop to about 10° to 15°. If O'Hare drops below 8° it will be the coldest we have been in nearly a year. The coldest low so far this winter was 8° on Christmas morning. The coldest temperature before that occurred on February 15th last year when the low dropped to 7°.






On The Snow Watch


Some snow is on the way this weekend starting late Saturday. The first round should wind down early Sunday morning followed by another round later Sunday into early Monday morning. Yet another shot at snow comes Monday afternoon into Monday night.


The GFS model cloud cover and precipitation meteogram shows those three main periods of potential snowfall.



The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. It suggests our first round late Saturday into early Sunday could squeeze out anywhere from a dusting to 1.5". The next round later Sunday into early Monday could lay down another dusting to up to 1.5" of snow. The third round on Monday could drop another half inch to nearly two inches. This meteogram shows a fourth round of snow later Wednesday into early Thursday with the potential for another dusting to a little over an inch.






Still Some Major Model Differences


When we add up all the possible snowfall the differences in the two major models becomes more apparent. The GFS model forecast spits out about 1" to 1.5" Saturday into the morning hours on Sunday.


The European model spits out less snowfall for the first system. It suggests a dusting to about a half inch Saturday night into the morning hours Sunday.




Grand Totals


Adding up all the possible snow through Tuesday morning on the GFS model shows a wide range of accumulation. The lightest amounts would be near the Wisconsin border with around 1.5" expected there. The heaviest amounts well south of the city with up to 9" possible. Most of us would be in the 2" to 6" range.


The European model has heavier amounts overall. It brings in more snow with Monday's system. The grand totals it spits out range from 2.5" near the Wisconsin border to 9" in the city and areas just south and west. Most of us would get about 5" to 9" in total according to this solution.


This is a complicated set up and there are many factors to consider that will shift these amounts and either increase or decrease the number of inches of snow that could fall. Some of the energy for these systems is just today coming ashore along the west coast. Models to this point have not gotten a good sample of the initial systems yet. A change in the track could also mean a changeover to freeing rain for some areas too. In other words, it's still relatively early so stay tuned. Snow is definitely coming but it's still too early to say exactly how much.






Mild End To This Month & Start To Next?


The long range temperature probability forecasts are hinting at a milder than average pattern for the end of this month and the first part of February. The 6-10 day temperature probability forecast has the Chicago area outlooked for about average temperatures overall from January 27th through January 31st. The longer range 8-14 day forecast keeps us favored for above average temperatures overall for the period from January 29th through February 4th.






Above Average Long Range Precip Pattern


The long range precipitation probability forecasts both favor us for above average precipitation overall. The 6-10 day forecast favors us for above average precipitation overall for the end of the month from January 27th through January 31st. The 8-14 day forecast has us outlooked for above average too. That forecast covers the period from January 29th through February 4tht.



The Climate Prediction Center just issued their revised forecast for February. It continues the same pattern that both the 6-10 day and 8-14 day outlooks suggest. We are outlooked for above average temperatures and precipitation overall for February.





Here is my 7 day forecast:


Today: Mostly sunny, breezy (single digit wind chills) High: 20


Saturday: Becoming cloudy, light snow develops late Low: 8 High: 28


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


Monday: Cloudy, periods of snow Low: 28 High: 35

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


Wednesday: Mostly cloudy, snow develops late Low: 22 High: 32


Thursday: Mostly cloudy Low: 23 High: 34


#ilwx

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