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  • Tim McGill

An Early Start To Summer?

Near 90° By Saturday Possible



The astronomical start of summer is actually June 20th this year but meteorological/climatological summer starts on June 1st. June, July and August are the three warmest months of the year on average in Chicago. It will feel just like July here before the week is over. Once the warm air arrives with highs in the 80s it could stick around through the end of the month based on long term forecasts. So it will be almost like starting summer nearly two weeks early.


Average highs for today's date are around 71°. Highs may be a few degrees cooler where the rain is most likely today south of I-80. Highs should be right around average today for most areas but cooler lakeside with a wind off the lake. Look for highs there to reach to near 60°.



We have a temporary setback with 60s for highs tomorrow but after that we'll enjoy a warm up right into the weekend. Highs could hit 80° by as early as Wednesday. 80s should continue through the weekend. Saturday's highs might get near 90°. That would be the warmest day we've seen since early September last year or over eight months ago.




The temperature anomaly forecast has most of the Midwest about 10° to 15° above average on Friday. That would mean highs at least into the middle 80s.


The GFS model surges Saturday's highs into the lower 80s north of Chicago and middle to upper 80s south of the city.





Need More May Showers


I mentioned in Saturday's post that the lack of rainfall this month at O'Hare could mean May makes its way into the record books. So far only .36" of rain has fallen this month. That is 2.01" below average. Since March 1st O'Hare is down 6.25" of rain compared to average.


The GFS model has several opportunities for more rain between now and Sunday. Most of today's rain will stay south of the city but there should be more widespread showers and even a few thunderstorms Tuesday into early Wednesday.



The GFS model keeps the significant rain today south of Chicago. Well south of the city the model spits out nearly an inch of rain. Along and south of I-80 there could be locally heavier rainfall than what is depicted by this model.



Running the precipitation accumulation forecast through Sunday yields a range of rainfall across the area. The heaviest total rainfall during that period would again be south of the city with an inch or even two possible and around three quarters of an inch of rain from Chicago and points northward.





Signal Strong For Warm End To May


The long range temperature probability forecasts continue to strongly signal an above average period overall for temperatures at the end of the month. The 6-10 day forecast favors us for above average temperatures overall from May 22nd through May 26th with Chicago's probability between 70-80%. The 8-14 day temperature probability forecast keeps us above average overall from May 24th through May 30th. 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.





Still Favoring Moist End To May

The longer range precipitation probability forecasts continue to signal an above average rainfall period for the end of the month. The latest 6-10 day forecast has Chicago favored for about average precipitation from May 22nd through May 26th. The longer range 8-14 day forecast has us favored for above average precipitation overall from May 24th through May 30th.




Here is my 7 day forecast:


Today: Cloudy, scattered showers mainly south High: 70 (60 lakeside)


Tuesday: Cloudy, periods of showers, sct. t-storm possible Low: 56 High: 68 (62 lakeside)


Wednesday: Sct. showers/t-storms early, mostly cloudy Low: 60 High: 79 (cooler lakeside)


Thursday: Spotty shower possible early, partly to mostly cloudy Low: 63 High: 84


Friday: Partly to mostly sunny, sct. shower/t-storm possible Low: 66 High: 85


Saturday: Partly to mostly sunny, sct. shower/t-storm possible Low: 67 High: 88


Sunday: Partly to mostly sunny, sct. shower/t-storm possible Low: 67 High: 88


#ilwx

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