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Weather Nerdy

So you thought it was fall? Why is it so hot in September?

Digital thermometer showing 95 degrees on a hot September day with fall leaves in the background.

Summer’s encore performance


Just when you thought you could bust out the sweaters and sip that pumpkin spice in peace...bam! Summer kicks down the door like, “Did you miss me?”


Across much of the U.S., it’s feeling more like backyard fireworks on the 4th of July than mid-September. Peoria, Illinois, hit 93° with a heat index of 96° Sunday, and the forecast keeps the low 90s rolling through the week. That’s about 20° toastier than normal, Mother Nature basically turned the oven back on.




The false fall fake-out


If you got tricked by the cool breeze last week, you weren’t alone. We had what’s known as a “false fall”, just enough chill to tease us into grabbing flannels and Insta-posting lattes. Now?


You’re sweating through that chunky sweater like it’s a bad fashion choice at a bonfire.


  • Minneapolis is aiming for 90°

  • Memphis is threatening 98° (record territory)

  • The Midwest and Great Lakes are sizzling like it’s peak July grill season



So why is it so hot in September?


People across the country are asking the same thing: why is it so hot in September when fall is supposed to be here?


Here’s the nerdy part: September usually means shorter days and a lower sun angle, the Earth is literally tilting us toward cooler weather. But the jet stream has soared into Canada, opening the gates for warm air to flood way north.


Combine that with a stubborn heat dome camped over the Midwest, and you’ve got yourself a September sauna.


Bonus misery? It’s dry. Central Illinois is already dealing with drought, and farmers have to watch for field fires during harvest. So, yes, we’re sweating and worrying. Fun combo.



Florida just shrugs


Meanwhile in Florida, 90s with a heat index pushing 100° is… well, Tuesday. But the real jaw-dropper is how far this heatwave has marched north. When Minnesota and Illinois are battling 90s in mid-September, you know summer just can’t let go.



So, when do we get a break?


Not until late this week. Highs stay above 90° through Thursday, with only slim rain chances until a slow-moving system drifts in. Even then, don’t expect a big soak — maybe half an inch at best.


And the Climate Prediction Center? They’re calling for above-average temps to hang on into next weekend.



Nerdy heat-wave factoids


  • September heat isn’t rare. Meteorologists even have a name for it: “Second Summer.” It’s when summer weather pops back up just before fall really locks in.

  • Records go big: St. Louis once hit 105° on Sept. 8, 1939, and Chicago reached 101° on Sept. 2, 1953. That’s triple-digit heat well after Labor Day.

  • It’s the sun, but not really: By mid-September, the sun angle is like late March, yet if the jet stream behaves just right, heat waves can feel like midsummer.

  • False fall vs. second summer: There’s a rhythm to it, first a cool snap tricks you into thinking it’s fall, then the atmosphere roars back with heat. Happens often enough that farmers and teachers joke about it.



Weather Nerdy bottom line: September promised pumpkins and cozy nights. Instead, it delivered sweat stains and AC bills. Classic summer move.

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