Deer Park, IL Weather

Key Messages

- Cooler with breezy northeast winds today, especially north of Interstate 80.

- Warmer temperatures in the low to mid 70s return by the middle of the week.

- A pattern change toward more opportunities for regular rainfall is set to occur toward the end of the week and into the first week of November.

Discussion

Issued at 233 AM CDT Mon Oct 26 2026

A surface cold front is beginning to shift southward into far northern Illinois early this morning. This front will bring a northeasterly wind shift as it settles into southern parts of the area by late morning and afternoon. Cooler air filtering into northern Illinois on breezy northeasterly winds will result in a cooler autumn day. Temperatures will top out only in the lower 60s across northeastern Illinois before falling back into the 50s by early evening. Inland and further south, temperatures will be warmer, with highs in the 70s expected south of I-80 into central Illinois and Indiana. Skies look to remain mostly cloudy today, starting with a brief period of low cloud cover (less than 900 feet AGL) this morning, followed by persistent higher-level clouds through the rest of the day.

On Tuesday, a series of mid-level impulses originating from northern Mexico are forecast to track northeastward into the lower Great Lakes, maintaining persistent mid- and high-level clouds across the area. The threat of rain remains very low due to dry low-level air; however, a few isolated sprinkles cannot be ruled out during the afternoon and evening from high-based showers. Potential impacts and confidence remain too low to warrant a formal mention in the forecast.

A large Canadian high pressure system will settle over New England by Wednesday. Flow around this high, combined with low pressure troughing over the Plains and Upper Midwest, will return mild southerly winds to the region. Consequently, temperatures will rebound back into the 70s area-wide by Wednesday. While warmer weather will persist through the remainder of the week, there is a chance for isolated to scattered showers and possible thunderstorms late Wednesday night into Thursday ahead of an approaching cold front.

Ensemble guidance continues to indicate a pattern change late this weekend into next week as a long-wave trough develops across the western United States. This pattern could bring increased rain chances to our region during and after the upcoming weekend.

KJB

Aviation

Issued at 1248 AM CDT Mon Oct 26 2026

Key messages for the 06Z TAF period:

* Sudden wind shift to NNE behind southward-moving cold front overnight

* IFR to LIFR cigs and MVFR vis following the wind shift into mid- morning. MVFR possibly lingering into early afternoon at MDW and especially GYY

A cold front is pushing south across far SE WI and approaching the state line as of this writing. A quick flip to NNE is anticipated behind the front. Some upstream sites have reported a period of NNE immediately i morning. This front will bring a northeasterly wind shift as it settles into southern parts of the area by late morning and afternoon. Cooler air filtering into northern Illinois on breezy northeasterly winds will result in a cooler autumn day. Temperatures will top out only in the lower 60s across northern its wake before NNE takes hold. Best guess on timing is between 08 and 09Z at RFD, 0830 and 09Z at ORD, and 0930 and 10Z at MDW.

A period of IFR to LIFR cigs is expected to set in an hour or two following the wind shift. A period of MVFR to IFR vis will be possible during this period as well. Confidence in cig/vis trends into Monday is somewhat low as upstream impacts have yet to materialize. IFR looks to clear out by mid-morning, although there is a signal for MVFR cigs to linger into early afternoon at MDW and especially GYY. For the time being, maintained a 16Z return to VFR in the MDW TAF while midday MVFR is forecast at GYY where confidence is higher.

Lot Watches

IL...None. IN...None. LM...Small Craft Advisory from 7 AM this morning to 7 AM CDT Tuesday for Winthrop Harbor to Wilmette Harbor IL.

Small Craft Advisory from 10 AM this morning to 7 AM CDT Tuesday for Wilmette Harbor to Calumet Harbor IL-Calumet Harbor to Gary IN.