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  • Tim McGill

Slow Warm Up Then Wintry Weather

Chilly Along Lakefront

Yesterday was the second straight day with below average temperatures at O'Hare. The last time we saw that was the first two days of this month. The month is still running nearly 8° above average despite those cooler days.

We have another cool to cold day today with a light breeze off the lake. It will be colder at the lakeshore with highs failing to climb above the 40s. Away from the lakefront our highs should climb into the middle 50s. The average high for today is 59°. Starting tomorrow, for the first time this spring our average highs will climb to 60°.

Still Watching For April Snow

The GFS model has not wavered in calling for rain late Monday night to change over to snow early Tuesday. I need to express some caution about the forecast for snow. It is still a long way off and very subject to change. It is looking a little more likely though that there will be some slushy accumulation at least on grassy surfaces.

We average 1.2" of snow for the month of April. The last significant April snow here was just two years ago when 2.5" of snow fell at O'Hare on the 27th of the month. It was the latest accumulating snow we had seen here in more than 25 years.

The accumulate snowfall meteogram for O'Hare shows a range of snowfall for early Tuesday morning. On the low end one model suggests a little over a dusting but on the higher end one model suggests nearly two and a half inches.

The GFS model keeps the swath of snow heavier snow mainly downstate where nearly 5" of snow could come down. We may miss the heavier snow but the model still brings a bit over 2" to snow in the city and nearly 5" well south and west of Chicago.

The European model had been running more stingy with the snow. The latest model run now suggest about three to four inches possible here.

Slow Warming Then Quick Fall

The hourly temperature meteogram compares many different forecast models. It shows a couple of cooler days today and tomorrow and then warming to near 60° for Sunday and Monday before a dramatic drop into the 40s for highs for Tuesday and Wednesday.

The temperature anomaly forecast suggests Tuesday morning could be the coldest period of the next seven days. It has northern Illinois and Indiana will be between 10° to nearly 20° below average. This arrival of colder air corresponds with arrival of some wet snow.

Weaker But Still Clear Cool Signal

The cooler signal in the longer range temperature probability forecasts isn't quite as strong as yesterday but it is still clearly favoring cooler temperature overall for the end of the month. The latest 6-10 day forecast has us outlooked for below average temperatures overall from April 21t through April 25th with the bullseye of the highest probabilities over northern Illinois. The 8-14 day temperature probability forecast has us favored for below average temperatures overall from April 23rd through April 29th too. Average highs in Chicago for late April are in the lower to middle 60s.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast is signaling a cooler than average end to April and a return to around average for the start of May. The temperature anomaly forecast for the week ending April 30th has us outlooked to be a bit below average overall. The forecast for the following week ending on May 7th has Chicago bouncing back to about average overall. Average highs by the start of May are in the lower 60s.

Trending From Dry To About Average Precip

The long range precipitation probability forecasts suggest we may move from a drier pattern to a more near normal pattern towards the end of April The latest 6-10 day forecast still has Chicago favored for below average precipitation from April 21st through April 25th. The longer range 8-14 day forecast has most of us outlooked for above about precipitation overall from April 23rd through April 29th.

Here is my 7 day forecast:

Today: Partly to mostly sunny High: 55 (48 lakeside)

Saturday: Partly to mostly cloudy Low: 38 High: 54 (48 lakeside)

Sunday: Partly to mostly cloudy Low: 39 High: 59 (49 lakeside)

Monday: Sunny early then clouds increase, rain late Low: 41 High: 61 (cooler lakeside)

Tuesday: Rain or snow early (some accumulation possible), mostly cloudy Low: 37 High: 46

Wednesday: Partly to mostly sunny Low: 34 High: 51

Thursday: Mostly sunny Low: 38 High: 59



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