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  • Tim McGill

August Ends With Possible Record Heat & September Starts Off Cooler

The summer of 2020's heat seems to have snuck up on us. With an average temperature of just over 76° (average temperature is high and low for the day divided by two) as of today this year is in a virtual tie with 1995 as the hottest summer on record (at least through August 23rd). Thus far there has only been one record high though and that occurred on June 2nd when O'Hare reached 94°.


The heat can't sneak up on us this week. Highs will be 10 to 15 degrees above average today through Thursday and a few records are in jeopardy.


Record High Forecast High


August 25 95° (2003) 94°

August 26 97° (1973) 95°

August 27 97° (1973) 96°


We will add even more 90-degree days this week. So far this summer there has been 25 of them. An average summer sees 14 90-degree days. By the end of this week we should be up to 29 which more than doubles that average. That would tie 1977 as the 4th most 90-degree days on record.


Highs today should reach into the lower 90s but a bit cooler along the lakefront with upper 80s there.


The longer rang forecast is hinting at a pattern shift towards cooler weather for the start of September. We'll take this with a grain of salt since I've seen this happen before to only see a continuation of above average temperatures. The 6-10 day and 8-14 day temperature probability forecast has us outlooked for cooler than average temperatures overall from August 29th through September 6th.



A somewhat dramatic drop in our temperatures is coming this weekend. By Sunday afternoon we should be 5 to 15 degrees cooler than average and around 15 to 20 degrees cooler than the middle 90s that will scorch us this week. The GFS temperature anomaly forecast for Sunday afternoon has a lot of blue over the Midwest which is an indication of a shift to cooler than average temperatures. That is something we have seldom seen this summer.


The longer range forecast for the week ending September 11th keeps that cooler pattern coming. Notice the blob of blue centered right over Illinois. This too shows we are favored for cooler than average temperatures overall for the start of next month.

We saw a few spotty showers and thunderstorms Sunday but more rain is needed to drop the rainfall deficit we have seen this summer. Both the 6-10 and 8-14 day precipitation probability forecasts have us outlooked for above average rainfall overall from August 28th through September 5th.




Here is my 7 day forecast:


Today: Mostly sunny High: 93 (89 Lakefront)


Tuesday: A.M. sct. t-storm then partly to mostly sunny Low: 73 High: 94 (85 Lakefront)


Wednesday: Mostly sunny Low: 73 High: 95


Thursday: Mostly sunny Low: 74 High: 96


Friday: Partly cloudy, sct. t-storms possible Low: 74 High: 86


Saturday: Partly to mostly sunny Low: 66 High: 82 (77 Lakefront)


Sunday: Partly to mostly sunny Low: 62 High: 80 (75 Lakefront)


#ilwx

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