Biggest Snow Of The Season So Far
Calm Before The Storm Most of Monday
We've been spared heavy snow so far this winter but that changes later today and tonight. We certainly have seen plenty of opportunities for snow. There have been 23 days this winter with snowfall reported at O'Hare. More than half of those days though the snow that fell was just a trace. There has been 7.9" of snow since December 1st. On average we should have 16.5" by now so we have seen less than half the normal snowfall.
This could be the biggest snowstorm in a little over two years. It could surpass the 5.3" that fell on January 28th & 29, 2019.
Snow will overspread the area from southwest to northeast this afternoon through this evening. The heaviest snow will fall between around 9 PM tonight through 2 AM Tuesday morning.
Most of the counties in pink have a winter storm warning from 4 pm today through 5 pm Tuesday. Most of the counties south of the city in blue have a winter weather advisory from 4 pm today through noon Tuesday. Those southern counties will have a mix of freezing rain, freezing drizzle and snow at times.
So much of Monday will actually be quiet. The storm's greatest impact will be tonight and early tomorrow but additional accumulation will come at times Tuesday afternoon into Wednesday.
Today's highs will be in the lower 30s but a brisk northeast breeze will make it feel like the teens and twenties.
Prolonged Period Of Snow
The GFS model cloud cover and precipitation meteogram shows accumulating snow from late today through most of Wednesday. That doesn't mean continuous snow the entire time. The heaviest snow will be late tonight into early Tuesday but there will be more light accumulation on and off through Wednesday afternoon. The main storm system snow will linger into Tuesday but lake effect snow will add additional accumulation Tuesday night and Wednesday.
The accumulated snowfall meteogram for O'Hare considers not just the GFS model but many different computer models. It suggests around 4" to just over 7" depending on the particular model. Most of this snow will be of the heavy and wet variety. We could see some blowing snow on Tuesday as the snow becomes lighter and the winds get stronger.
Models More In Agreement
I've been tracking this storm for several days since it first began to form off the California coast and then eventually moved onshore. The models initially did not agree with the amount of snow that would come and exactly where it would fall. The last few model runs have brought more consensus.
The GFS model forecast spits out about 5" to 7" of snow total between today and Wednesday morning. Most of that snow coming late today through early Tuesday.
The European model has similar amounts in the forecast for the same period. Lighter amounts well south of the city where a mix of precipitation at times will limit the snowfall a bit.
The NAM or North American Model also suggests around 5" to 7" total for most of northern Illinois.
Winds To Whip Up Big Waves
A lakeshore flood advisory is in effect for Lake, northern and central Cook counties in Illinois and Lake county Indiana from 4 pm today through noon Tuesday. Winds could gust to near 40 mph during that time and whip up waves as big as 8 to 13 feet.
Mild Start But Cold Finish To February?
The long range temperature probability forecasts have us favored for a relatively mild start to February. The 6-10 day temperature probability forecast has the Chicago area outlooked for above average temperatures overall from January 30th through February 3rd. The longer range 8-14 day forecast drops those probabilities a bit but keeps us favored for above average temperatures overall for the period from February 1st through February 7th.
The even longer range Subseasonal Experiment (SubX) forecast suggests colder air could be coming for the middle part of February. The forecasts for both the week ending February 12th and the week ending February 19th have us favored for below average temperatures overall. The drop from average gets a little more dramatic the further into February we go.
More Active Precip Pattern Could Continue
The long range precipitation probability forecasts keep the precipitation pattern active through the first part of February. The 6-10 day forecast favors us for above average precipitation overall from January 30th through February 3rd. The 8-14 day forecast has us outlooked for above average precipitation overall from February 1st through February 7th too.
Here is my 7 day forecast:
Today: Cloudy, blustery with snow developing from south to north this afternoon High: 33
Tonight: Snow, heavy at times, windy Low: 32
Tuesday: Snow tapers off by the afternoon, blustery, near steady temps High: 34
Wednesday: Mostly cloudy, on & off snow showers Low: 24 High: 29
Thursday: Partly to mostly sunny Low: 9 High: 25
Friday: Partly to mostly sunny Low: 12 High: 30
Saturday: Mostly cloudy, rain develops late Low: 25 High: 40
Sunday: Light rain/snow possible early, mostly cloudy Low: 30 High: 35