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Every Year in Chicagoland

Chicago's record October heat and the cold snap behind it

O'Hare hit a record 88°F on Oct. 12. Here's why it happened, how rare it is, and the day-by-day forecast as a cold snap moves in.

By HellginOctober 14, 20266 min read

If you spent Monday with the windows open and the AC humming, maybe with the pumpkins already sweating on the porch, the heat was real. O'Hare hit 88 degrees on Monday, Oct. 12, a record for the date. It won't last. A cold front comes through midweek, and by Friday and Saturday the area gets its coldest air of the season so far. Here's how rare Monday was, what caused it, and what each day this week looks like.

The record, and what's coming next

O'Hare reached 88°F by 4 p.m. Monday, Oct. 12, 2026, a new record high for the date, according to Block Club Chicago and the Chicago Sun-Times. That's mid-July weather showing up in the middle of fall.

The cold arrives quickly after it. The National Weather Service in Chicago said the record warmth will give way to the coldest air mass of the season by Friday and Saturday. Highs will be in the 50s, and lows will be in the 30s away from Chicago and Lake Michigan, Block Club reported. The weather service posted the same forecast.

The lake matters here. Lake Michigan is still holding summer warmth, so the city and the lakefront usually stay a few degrees milder on cold nights than the suburbs and the far-out counties. If you live out in the Fox Valley, or anywhere well away from the lake, you're the one who should plan for the coldest nights.

The cold snap won't last long either. The weather service expects warm weather to come back next week. Before that, though, you'll get a summer day, storms, a front, and the first chilly nights of fall, all within about five days.

How hot it got, and how rare that is

The old record for Oct. 12 was 84°F, set in 2008, according to the Sun-Times and Block Club. Monday beat that mark by four degrees. Daily records usually fall by a degree or so, so four is a lot.

Block Club also reported that Monday tied for the second-warmest day this late in the fall since Chicago's records began in 1871. That means very few days in more than 150 years of record-keeping have been this hot this late in the season.

It still wasn't the hottest October day ever. That record is 94°F, set on Oct. 6, 1963, and it still stands. The 1963 heat also came a week earlier in the month, when the sun is a bit higher and summer heat is easier to hang on to. Reaching 88 on Oct. 12 is harder.

Another record could be close on Tuesday. The record high for Oct. 13 is also 88°F, and Block Club reported that some parts of the area could get near it. The Sun-Times forecast is cooler, with highs in the upper 70s. Either way, Tuesday is expected to be the last day this week that's warmer than normal.

Why it happened

Here's the short answer. "We had a pretty pronounced ridge with the jet stream across the eastern United States," National Weather Service meteorologist Jake Petr told the Sun-Times.

The jet stream is the fast river of air high above us that separates cold northern air from warm southern air. When it bends north into a ridge, the warm air underneath can push much farther north than it usually does in October. That ridge let a warm air mass from the south, as Block Club described it, reach all the way to northern Illinois.

The ridge also explains the cold that follows. Once the jet stream flattens out or dips, the warm air gets pushed out and cooler air from the north moves in behind a cold front. That's the swing you'll feel this week.

Day by day this week

Tuesday: One more warm day. The Sun-Times expects highs in the upper 70s. Block Club said some spots could get near the 88-degree record for the date. Tuesday night brings thunderstorms, with a small chance of hail, per Block Club, which 94.7 WLS also carried. If you have patio furniture, lawn decorations or an inflatable ghost already up in the yard, bring them in or tie them down before bed.

Wednesday: The storms should clear by morning, and then the cold front comes through. Highs drop into the 60s, according to the Sun-Times. By Wednesday night temperatures fall to the mid-50s, according to Block Club and Time Out Chicago. That's more than 30 degrees colder than Monday afternoon.

Thursday: Showers last into the afternoon, with highs in the low 70s, according to both Block Club and Time Out. It's a damp day, but not cold yet. Grab an umbrella rather than a winter coat.

Friday and Saturday: This is when the real cold arrives. The weather service expects highs in the 50s on both days. Friday night could drop into the 30s. Time Out puts the low in the upper 30s, and the coldest readings are expected away from the city and the lake. Saturday morning will be the chilliest start of the fall so far. It's a good weekend for a hoodie at the pumpkin patch or a jacket at the Friday night football game.

What to expect after

With lows in the 30s outside the city, frost is possible Friday night, especially in open, rural areas and low spots far from the lake. If you still have tomatoes, peppers, basil or potted annuals outside, Friday afternoon is a good time to pick them or cover them. Check the National Weather Service Chicago office on Friday for any frost or freeze advisory in your county.

By Chicago standards, an early frost wouldn't be unusual. A Fox 32 report puts O'Hare's average first fall freeze around Oct. 13 and Midway's around Oct. 23. Midway's later date comes from more pavement and buildings around the airport, which hold heat at night.

Then the warmth comes back. The weather service expects unseasonably warm weather to return next week and into next weekend. "It's going to be ups and downs as far as temperatures go," Petr told Block Club. Don't put the shorts away yet, but get the jackets out where you can reach them, too.

Sources (7)

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