Brace For Biggest Snow Of Season So Far
May Be Biggest Snow In Over 2 Years
The 6" of snow that fell early last week was the biggest two day total since 8.4" fell on November 25th and 26th back in 2018. This weekend's storm could rival that bigger total. One thing is certain, we will bring our total snowfall for this season back up above average by the time the weekend is over. O'Hare has seen 13.9" of snow since December 1st. In an average winter we would have 18.2" by today's date. We will more than make up for that deficit between today and tomorrow.
The accumulated snowfall meteogram for O'Hare considers many different computer models. It suggests a range of 4" to 8" of snow for our first round of snow late today into tonight. Some additional accumulation (1" to 3") will fall during the day on Sunday. That is indicated by the smaller "bump" just after the first big one. The second bigger bump for next Friday into Saturday suggests another storm that could dump several inches of snow. That second storm is still far off and will have to be watched closely because a lot could change between now and then.
My final snowfall forecast is calling for 4" to 8" by Sunday morning with the bulk of that falling between 6 pm today through 3 am tomorrow. An additional 1" to 3" is possible on Sunday but will be spread out through the day. In total that means around 5" to 10" with a few spots even close to a foot of new snow.
Timing It Out
Snowfall with today's storm will nudge north and east across northern Illinois starting mainly late this afternoon. The National Weather Service has an outline of the onset times for our area. Snow or a mix will start to fall by mid-afternoon well southwest of the city and finally reach Chicago late this afternoon or early this evening.
A winter storm warning begins for most of us at 3 PM today and lasts until 6 pm Sunday. Counties shaded in pink are under a warning. Counties shaded in blue have a winter weather advisory. For areas well southwest of the city it begins at noon. In addition, a lakeshore flood advisory is in effect today through 3 AM on Monday.
Models More In Agreement
The confidence in the snowfall forecast for this weekend started to increase a few days ago. The models were beginning to come more into consensus.
I'm going to look specifically at three different models. While there are some minor variations, they all agree several inches of snow will fall this weekend. The total snowfall through Monday morning from all three models is roughly in the range of 7" to 10". Snowfall rates could reach about 1" to 2" an hour for a period late this evening into early Sunday morning.
The GFS model spits out anywhere from a little over 7" to a little over 10" with the highest amounts in the city and areas just south and west. These totals include today, tonight and tomorrow's total snowfall accumulation.
The European model spits out nearly 7" to almost a foot. It has the heaviest snow south of the city.
The NAM model has six inches to a little over a foot. Heaviest amounts are again south of the city with this model. Those heaviest amounts south and southwest of the city may be a bit overdone on some of these models since some rain or a mix at the onset of the storm will probably occur in those areas which would limit the snowfall totals.
Gusty winds, first out of the southeast and then shifting to the northeast, could complicate things too. They will reduce visibilities throughout the duration of the storm and cause some blowing and drifting snow mainly early Sunday.
Looking Longer Range At More Snow
I ran out the GFS model and European model's snowfall accumulation forecast through next weekend. They both hint at another potentially big storm next Friday into early Saturday. These snowfall numbers have to be adjusted to determine how much of these totals will be from Friday's storm only. My estimate (after subtracting this weekend's totals) from the GFS model means about 2" to 6" is possible late next week. Once again I have to caution that this is preliminary and very much subject to change.
After subtracting this weekend's totals from the European model forecast for total accumulation through next weekend, it looks like it is projecting anywhere between a couple of inches to nearly 10 inches for Friday into Saturday but keeping the snow a bit further north in our area.
Blob Of Blue Gets Bigger
The "blue blob" is getting bigger on the long range temperature probability forecasts and expanding further eastward. More of the country is forecast to be below average overall for the first part of February and that includes Chicago. The latest 6-10 day temperature probability forecast has the Chicago area outlooked for below average temperatures overall from February 4th through February 8th. The longer range 8-14 day forecast keeps the colder air coming overall from February 6th through February 12th.
The even longer range Subseasonal Experiment (SubX) forecast suggests seems to support a change to a colder pattern is 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.
Active Pattern May Continue
The long range precipitation probability forecasts keep the precipitation pattern active through almost the middle of next month. The 6-10 day forecast favors us for above average precipitation overall from February 4th through February 8th. The 8-14 day forecast has us outlooked for above average precipitation overall (although the probabilities drop just a bit) from February 6th through February 12th too.
Here is my 7 day forecast:
Today: Cloudy, becoming blustery, snow develops late (mix possible south) High: 34
Tonight: Snow (heavy at times), blowing snow, windy with near steady temps High: 31
Sunday: Blowing & drifting snow early, cloudy with additional light High: 32
Monday: Mostly cloudy Low: 27 High: 34
Tuesday: Partly to mostly sunny Low: 17 High: 32
Wednesday: Partly to mostly cloudy Low: 20 High: 35
Thursday: Mostly cloudy, light rain or snow late Low: 32 High: 38
Friday: Cloudy, snow possible Low: 21 High: 28