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  • Tim McGill

About To Flip The Switch To Summer

Updated: May 19, 2021

Warmest Weekend Since August?

Meteorological summer starts in just under two weeks but we will soon be seeing more typical temperatures for the middle of July. Highs this weekend may even tag 90° in a few spots. It should be the warmest weekend here in nearly nine months.

We have one more about average day before we start to crank up the heat and humidity. Today's highs should climb into the lower to middle 70s in most areas but only lower to middle 60s along the lakefront.

A component of the wind will be off the lake through early Wednesday morning. That means we will be around 10° cooler lakeside today but by Wednesday afternoon the winds shift more southerly and warmer air will sweep all the way through the lakeshore. It will be breezy both today and tomorrow with gusts to 30 mph. Showers should stay south and west of the city early today but rainfall chances ramp up late this afternoon and stay fairly high through the first part of Wednesday.

Starting Wednesday highs will be 80° or warmer through at least Monday. The last time we strung together six straight days that warm was in early September last year.

May started off warm with a weekend of 80s but then a cooler pattern kicked in. Eleven of seventeen days this month have been below average and the month is now running nearly 3° below average overall. Forecast models are strongly suggesting an overall warm end to the month that should eat away at that temperature deficit quickly.

The temperature anomaly forecast has most of the Midwest about 10° to 15° above average on Saturday. That would mean highs at least into the middle 80s. Average highs for Saturday's date are around 73°.

Sunday should be fairly steamy too. The GFS model surges Sunday's highs into the middle to upper 80s. The last time we saw a weekend this warm was back on August 22nd and 23rd last year when highs hit 89° and 92° respectively.

Not Enough Rain To Put Dent In Drought

The rainfall deficit for the month of May and the entire season of spring grew again yesterday. So far O'Hare is 2.16" of rain below average this month an 6.43 inches of rain below average since March 1st.

The GFS model has still shows several opportunities for more rain over the next couple of weeks but it's not the more widespread drenching rain needed to put a dent in the drought.

The GFS model precipitation accumulation forecast through Monday morning spits out between a third of an inch south of the city to just under an inch of rain west of the city to three quarters of an inch north of Chicago.

Finishing May On The Warm Side

The long range temperature probability forecasts once again are showing a fairly strong signal for a warmer than average end to May. The 6-10 day forecast favors us for above average temperatures overall from May 23rd through May 27th with Chicago's probability between 60-70%. The 8-14 day temperature probability forecast keeps us above average overall from May 25th through May 31st. Average highs for this period are in the lower to middle 70s.

The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast is favoring the Chicago area for a slightly cooler than average last few days of May and first few days of June overall. The average highs for this period are in the middle to upper 70s. The temperature anomaly forecast for the week ending June 4th has us outlooked to be just a smidge below average overall. The forecast for the following week ending on June 11th has Chicago about average overall.

Odds Increase For More Rain

The longer range precipitation probability forecasts for the past several runs have been consistently calling for above average precipitation. The latest run is no exception and it even increases the probabilities a bit. The latest 6-10 day forecast has Chicago favored for above average precipitation from May 23rd through May 27th. The longer range 8-14 day forecast has us favored for above average precipitation overall from May 25th through May 31st as well.

Here is my 7 day forecast:

Today: Mostly cloudy, showers mainly late, t-storm possible south High: 73 (64 lakeside)

Wednesday: Sct. showers/t-storms mainly early, mostly cloudy Low: 62 High: 79

Thursday: Cloud & sun mix, spotty shower or isolated t-storm possible Low: 64 High: 85

Friday: Cloud & sun mix, warm & humid Low: 67 High: 86

Saturday: Partly to mostly sunny Low: 67 High: 89

Sunday: Partly to mostly sunny, sct. shower/t-storm possible Low: 68 High: 88

Monday: Partly to mostly sunny, sct. shower/t-storm possible Low: 66 High: 87



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