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  • Tim McGill

Summer Is Spilling Over Into Fall More & More

Fall is my favorite season. Meteorologically speaking it started on September 1st. I've been warning about a dramatic drop in temperatures for the first part of fall this year. More on that below. Fall has been changing over the years. On average there are more fall days that seem more like summer.


Summer heat is spilling over into fall more and more lately in Chicago. Since 1970 there has been an increase of 6 days with above normal temperatures here in fall. Chicago's falls are now just under 1° warmer compared to 1970. Climate Central points out the consequences of a warmer fall:


  • Higher cooling demands

  • Longer mosquito and tick season

  • Extended pollen season



The conditions where mosquitoes thrive are extending further into fall with that increasing warmth. The annoying pests do best with temperatures between 50° and 95° with a relative humidity of 42% or more. That means our warmer falls are now producing an additional 16 "mosquito days" compared to the 1980s.



Climate Central analyzed 242 cities and found 95% of them had in increase in their average fall temperature since 1970. More than half of those cities saw in increase of more than 2°. The greatest fall warming was in the Rockies and southwest. The upper Midwest, Great Lakes and Northeast also saw more significant warming.



Speaking of above average fall days...


We've started off this fall about 5° above average so far. It will feel just like July with highs today reaching into the middle 80s.


A gusty southwest wind will help push those highs to summer like levels. The hourly forecast shows gusts over 30 mph starting around midday and continuing into the afternoon.


Models are not in total agreement on just how dramatic a drop in temperatures could be coming next week. The GFS model is a bit more aggressive in bringing in cooler air. The GFS temperature anomaly forecast has most of the middle of the country well below average next Wednesday afternoon. Some spots in the Midwest could be nearly 30° or more below average.

The model has a wide range of temperatures in our area next Wednesday afternoon. From our northwest suburbs to northern Indiana there is about a 20° spread. It could be as cool as the 50s northwest of the city with 60s in the city itself and milder 70s in northern Indiana.


O'Hare picked up a paltry .05" of rain on Wednesday. Since July 1st we are officially down over 5 inches of rain compared to average. There is a slight chance for a spotty shower today but the chances of rain ramp up Saturday night into Sunday. Looking longer range the best chance of rain is later next Tuesday into Wednesday.


The long range temperature probability forecasts continue to cool us off next week and into the middle of the month. Both the 6-10 day and 8-14 day forecasts have us outlooked for below average temperatures overall from September 8th through the 16th.


The longer range precipitation probability forecasts suggest a more soggy period followed by near normal rainfall. The 6-10 day forecast has us outlooked for above average precipitation from September 8th through the 12th. The 8-14 day forecast has us with around average rainfall from September 10th through the 16th.



Here is my 7 day forecast:


Today: Partly to mostly sunny, breezy High: 86 (temps fall late into the 70s)

Friday: Mostly sunny Low: 58 High: 78


Saturday: Mostly sunny Low: 60 High: 83


Sunday: Partly to mostly cloudy, sct. showers & t-storms Low: 63 High: 82


Monday: Partly to mostly cloudy Low: 63 High: 80


Tuesday: Mostly cloudy, sct. showers Low: 64 High: 70


Wednesday: Mostly cloudy, sct. showers Low: 61 High: 72

#ilwx

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