NWS Forecast for O'Hare International Airport Chicago, IL Last Update: 2:26 pm CDT Oct 10, 2024

Thursday Afternoon: Sunny, with a high near 73. East wind around 10 mph.

Thursday Night: Clear, with a low around 54. East wind around 5 mph becoming south southwest after midnight.

Friday: Sunny, with a high near 85. Southwest wind 10 to 15 mph, with gusts as high as 25 mph.

Friday Night: Mostly cloudy, with a low around 56. Southwest wind 10 to 15 mph becoming northeast after midnight. Winds could gust as high as 25 mph.

Saturday: A 30 percent chance of showers, mainly after 1pm. Mostly sunny, with a high near 68. Northeast wind 10 to 15 mph, with gusts as high as 20 mph.

Saturday Night: A chance of showers and thunderstorms before 10pm, then a chance of showers between 10pm and 1am. Mostly cloudy, with a low around 54. Chance of precipitation is 30%.

Sunday: Mostly sunny, with a high near 65.

Sunday Night: Partly cloudy, with a low around 44. Columbus Day: A chance of showers after 1pm. Mostly sunny, with a high near 55.

Monday Night: A chance of showers before 1am. Partly cloudy, with a low around 39.

Tuesday: Sunny, with a high near 55.

Tuesday Night: Mostly clear, with a low around 39.

Wednesday: Sunny, with a high near 61.

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

256 PM CDT Thu Oct 10 2024

.KEY MESSAGES...

- Dry, breezy, and unseasonably warm on Friday with an elevated   brush fire risk.

- Scattered showers possible Saturday afternoon and evening.

- A notable cool-down early next week with the potential for   nightly frost and localized freeze conditions, along with lake   effect showers downwind of Lake Michigan.

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.DISCUSSION... Issued at 256 PM CDT Thu Oct 10 2024

Through Friday Night:

With dew points in the 30s and lower 40s this afternoon and clear skies and light winds tonight, undercut raw model guidance for forecast lows and leaned toward MOS guidance. Expecting mid to upper 40s (localized lower 40s) outside of Chicago and mid to upper 50s in and near the city.

Friday will be the peak of the warmth in our latest stretch of dry conditions with well above normal temperatures. After a clear and cool start to the day, summer-like warmth is in store for the afternoon. Forecast high temperatures in the 80-86F range coinciding with breezy southwest winds gusting up to 25-30 mph and dew points mixing out to ~45-50F should translate to an elevated risk for a more rapid spread of brush and grass fires. Consider postponing any planned outdoor burning and use plenty of caution when disposing of smoking materials.

A fairly stout backdoor cold front will shift south across most of the area Friday night, the first sign of the impending notable cool-down coming later in the weekend. Breezy north- northeast winds north of I-80 behind the front will be strongest near the lake, with gusts up to 25-35 mph.

Saturday through Thursday:

The front will become quasi-stationary across our far southern CWA on Saturday, separating seasonably mild conditions (60s and 70s) I-80 and north/coolest closer to the lake from one more day of summer-like upper 70s to lower 80s well south of I-80.

Recent model guidance cycles have varied run to run regarding column moisture availability mid day Saturday through the evening. A robust short-wave trough over the northern Great Lakes will spread mid-level height falls across the lingering elevated frontal zone north of the quasi-stationary front. In the 12z cycle, there was a trend back toward sufficient moisture for scattered showers developing, with possibly even a few isolated embedded thunderstorms in the evening, for the northeast half or third or so of the CWA. Also contributing in this setup should sufficient moisture materialize will be the tightening thermal gradient aloft (frontogenesis) and fairly steep mid-level lapse rates. For this afternoon`s issuance, PoPs peaked in the 30-40% range Saturday evening.

A stronger reinforcing cold front will force the original stalled frontal zone southward on Sunday, knocking temperatures down inland about 5-10 degrees vs. Saturday. Breezy northwest winds behind the front will gust up to 30-35 mph. Looking at a favorable thermodynamic setup for lake effect showers downwind of Lake Michigan Sunday night, primarily for northeast Porter County and points east. Aside from the lake effect potential, Sunday night will be chilly with lows in the 30s and 40s and gradually subsiding northwesterly breezes adding to the chill.

A final even more pronounced push of cool air will arrive on Monday behind yet another reinforcing cold front. Mid-level impulses pivoting around the western periphery of deep troughing over northeast North America may support the development of isolated to scattered showers Monday afternoon. Forecast highs are only in the mid to upper 50s! An even more favorable thermodynamic setup for lake effect showers is probable Monday night, with a prevailing 340-350 deg wind direction favoring Lake and Porter Counties down to near or just south of the Kankakee River.

The bigger story for the rest of the area (outside of Chicago) is the likelihood of the first good frost and localized freeze setup, as low temperatures dip into the lower to mid 30s both Monday and Tuesday nights. Barring a big change in the setup, or more cloud cover, frost/freeze headlines are a decent bet. Tuesday`s highs will only be in the lower to mid 50s, albeit with plenty of sunshine underneath surface high pressure. Medium range indicators favor a return to above normal temperatures and dry conditions mid to late next week and beyond.

Castro

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.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/... Issued at 1217 PM CDT Thu Oct 10 2024

Southwest winds will increase Friday morning, likely becoming gusty midday and into the afternoon Friday. VFR conditions are expected through the TAF cycle.

- Izzi

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.LOT WATCHES/WARNINGS/ADVISORIES...

IL...None.

IN...None.

LM...None.