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  • Tim McGill

Some Spring Snow In The Forecast

Some Sunshine Today

We will have a couple shots at snow next week. Nothing to worry about today though. Some sunshine and a west breeze today should push our highs to around 10° above average. It will be cooler right along the lakefront but most areas should see highs in the middle 50s. March is running 9° above average so far.

Colder Air Coming

Temperatures will be falling through Monday but no signs of the polar vortex that made February so frigid. 50s today then falling into the 40s for highs Sunday and dropping into the 30s by Monday. Gusty winds will develop Sunday and linger into Monday so wind chills will drop from the 30s on Sunday into at least the 20s by Monday.

Two Shots At Snow

Yes, we normally have snow in March. We are now running nearly 3" below average. The average March sees nearly a half a foot of snow. The latest GFS model's meteogram shows a wintry mix on Monday with most of the precipitation coming in the form of wet snow. The second system of the week arrives later Wednesday initially as rain and then changes to snow on Thursday.

The accumulated snowfall forecast meteogram shows several different model solutions for snowfall next week. The first round has a range of a dusting to nearly 3" with most of that coming later Monday. The second round has a range of a dusting to nearly 4" with most of that snow falling early Thursday.

The latest GFS model snowfall accumulation forecast through early Tuesday lays down about an inch to 3" in northern Illinois. Heavier snow could target northern Iowa with up to 8" possible.

I ran out the model through Thursday morning to capture the second round of snow. The total snowfall accumulation through that period is between a couple of inches south of the city to nearly a foot well north and west of Chicago. After subtracting the first round it would suggest this second system would squeeze out about an inch or two to nearly 10". There is even a pocket of northwest Illinois that would see nearly two feet of snow in total through Thursday morning.

The European model is now in more agreement with the GFS. It squeezes out about an inch to nearly 3" with the first round of snow that falls mainly on Monday.

The models diverge when it comes to the second system. The European model keeps the accumulating snow with this system well south of the city and does not add any significant snowfall to our area through Friday morning.

The fact that these models are coming more into consensus on the first system gives me a little more confidence in the snowfall forecast for Monday into early Tuesday morning. Even still, there will be some very dry air that the first system has to first overcome before we can get snow to fall. Models sometimes overdo it with snowfall in these scenarios. The second system is even more difficult to call at this point because of the lack of model agreement. So as I like to say, stay tuned!

Wind Could Bring Big Waves

As mentioned above, winds will pick up in speed on Sunday and stay gusty into Monday. This could lead to at least some minor lakeshore flooding for portions of Cook and Lake Counties in Illinois.

Mild End To March

The long range temperature probability forecasts signal for a relatively mild end to March is getting a bit stronger. The latest 6-10 day temperature probability forecast has us outlooked for above average temperatures overall from March 18th through March 22nd. The longer range 8-14 day has us favored for above average temperatures overall from March 20th through March 26th too with slightly higher probabilities. We are again on the low end of probabilities so the signals aren't very strong.

The even longer range Subseasonal Experiment (SubX) forecast brings a milder end to March. The temperature anomaly forecast for the weekend ending March 26th has us outlooked to be around average for the week. The forecast that looks at the end of March and the start of April has us returning to above average temperatures overall for the week ending on April 2nd.

Weak Precipitation Signal

The longer range precipitation probability forecasts suggest we start out relatively dry and become relative wet but the probabilities for both forecasts are on the low end. The latest 6-10 day forecast has us outlooked for below average temperatures overall from March 18th through March 22nd. The longer range 8-14 day forecast has northern Illinois outlooked for above average average precipitation overall from March 20th through March 26th. The risk for spring flooding is above average for many area rivers. More on that below.

Springing Forward

The Climate Prediction Center's seasonal forecast for spring suggests a mild and moist pattern overall here. The temperature probability forecast for the months of March, April and May have us outlooked for above average temperatures overall. The precipitation probability forecast for the same period has us outlooked for above average precipitation overall.

Spring Flood Risk Forecast

The National Weather Service considers many risk factors for spring flooding. They include snow cover, soil moisture, and current river conditions.

"A significant snow cover with high water content can increase the chances of flooding once warmer weather melts the snow. Elevated soil moisture conditions reduce the amount of rainfall that is soaked up by the ground and increase the amount of water that then runs off into area streams. Above average river levels reduce the river rise required to reach flood stage, while below average river levels would require an increased amount of river rise to reach flood stage."

Their latest forecast suggests the flood risk is above average for many of our area rivers. The Des Plaines and Fox rivers in particular need to be watched closely.

Here is my 7 day forecast:

Today: Partly to mostly sunny High: 56 (45 lakefront)

Sunday: Mostly cloudy, becoming windy Low: 37 High: 48 (cooler near the lake)

Monday: Cloudy, chance of rain and snow (accumulation possible), blustery Low: 32 High: 39

Tuesday: Partly to mostly cloudy Low: 32 High: 46

Wednesday: Mostly cloudy, chance of rain and snow late Low: 32 High: 48

Thursday: Cloudy, chance of rain and snow (accumulation possible) Low: 31 High: 45

Friday: Partly to mostly sunny Low: 32 High: 46



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