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  • Tim McGill

Second Half Of Winter Starts With Snow

So Far So Good


Congratulations! We have officially passed the half-way point of winter. Yesterday was our 45th day of the season and including today, we have 45 more to go. All things considered, the first half has been a breeze so far.


On average the coldest point of winter is the four day period from January 17th through the 20th. The daily average temperature (average high added to average low and dived by two) is 23° during this stretch. While most of the western half of the country has passed the typically coldest part of its winter, we are just approaching ours.

We saw a trace of snow officially at O'Hare Thursday to bring the snowfall total for winter so far to 4.7". We are more than 8" below average. The average snowfall for winter to date is 12.8". We have had several days with snowfall reported so far this season. Nearly one out of every three days this winter has seen snow but the amounts have been very light. There has been just a trace of snow on 10 of the 15 days with snowfall so far this winter.


Temperatures haven't been too terrible either. We have seen only six days with highs less than 32°. We have yet to see a day with temperatures falling below zero. December was 5.1° above average overall and January is now running 7.5° above average.

Today will be the 21st straight day with above average temperatures. Highs should top out in the middle to upper 30s.



Temperatures finally fall after today and may bump just below average by Monday or Tuesday. Even though we will turn a little colder there is still no signs of any bitter blasts of Arctic air for the next seven days.






On & Off Snow This Weekend


We have several chances at snow between today and early Monday morning. The GFS model cloud cover and precipitation meteogram shows occasional snowfall for the next three days. Most of us won't see huge totals but there could be a few spots that see several inches of accumulation. There could be snowfall rates of 1" to 2" per hour for a limited time in isolated areas. It won't be widespread but it could lead to some rapid accumulation for some.



The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. It shows three main periods that favor snowfall. The first is this afternoon with snow showers likely. The second is Saturday morning. The third late Sunday into early Monday morning. I boxed the periods that show bumps by the models representing periods with at least minor accumulations possible.






Adding It All Up


The GFS model forecast spits out a grand total of about 1" to 3" for most of us from 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 north central Indiana.



The European model is calling for similar snowfall overall during the same period. It spits out about 1.5" to nearly 4" in total. I think the grand total for most areas will fall in the 1" to 3" range but there could be a few spots where 3" to 6" possibly pile up.


ECMWF Model Total Accumulated Snowfall Forecast Through Monday Afternoon (Pivotal Weather)




Arctic Cold Coming?


There are some hints of some harsher winter weather in the longer range forecasts. We've been spared from any real Arctic air so far but that could change in a couple of weeks. Previous blog posts have warned about a possible upcoming shift to a much colder pattern. A recent "sudden stratospheric warming" could jostle the polar vortex and send some lobes of Arctic air our way.


We cold be flirting with some frigid air next Friday. The temperature anomaly forecast for next Friday morning shows northern Illinois anywhere between 5° to 15° below average. That would mean lows that morning at least in the single digits.


The GFS model brings in even colder air in about ten days from now. Look at the forecast temperatures for the morning of January 26th. It has northern Illinois plunging to anywhere between -3° to -12°. That would be the coldest morning we have seen in nearly a year. The last time we dipped below zero was on February 14th last year when the mercury dropped to -2°. It is still a long way off but this model has been calling for much colder air coming at some point within the next two weeks.





Chilly End To Month?


The longer range temperature probability forecasts have us trending from near or above average overall to below average overall. The 6-10 day temperature probability forecast has the Chicago area split in two. The city and nearby suburbs are outlooked for above average temperatures overall from January 20th through January 24th. Our western suburbs are favored for around average temperatures. The longer range 8-14 day forecast all of northern Illinois outlooked for below average temperatures overall for the period from January 22nd through January 28th. There is a lot of blue on the map all the way westward to the west coast. Time will tell if those darker blues continue to spread towards us which would indicate even higher probabilities of colder than average temperatures could be coming for the end of January and the first part of February.






Area Of Green Has Grown


Our long range precipitation probability forecasts has plenty of green on it. Those green shades depict areas of the country where above average precipitation overall is favored. The 6-10 day forecast from January 20th through January 24th has us outlooked for below average precipitation overall. The 8-14 day forecast keep us outlooked for above average precipitation from January 22nd through the 28th. A lot of this precipitation could fall in the form of snow if the longer range temperature forecasts verify.






Here is my 7 day forecast:


Today: Cloudy, on & off show showers, a bit breezy High: 38


Saturday: On & off light snow, breezy Low: 29 High: 38


Sunday: Cloudy, light snow mainly late Low: 28 High: 32


Monday: Partly to mostly cloudy Low: 24 High: 31


Tuesday: Mostly cloudy Low: 25 High: 32

Wednesday: Partly to mostly sunny Low: 19 High: 33


Thursday: Partly to mostly sunny Low: 22 High: 30


#ilwx

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