textproduct: Chicago

KEY MESSAGES

- Patches of fog and low clouds will persist early this morning.

- A period of rain is possible this afternoon and evening, primarily in areas south of the Illinois and Kankakee rivers.

- Following a period of warmer weather over the weekend, widespread rain is likely (70%+ chance) late Monday into Tuesday.

- Turning much colder for Thanksgiving.

DISCUSSION

Issued at 225 AM CST Fri Nov 21 2025

Some early morning fog continues in advance of a weak cold frontal boundary shifting into the area. However, much of the dense fog (visibilities <1/4 mile) has been confined south of the area in central and southern IL and IN. If these trends continue, we will likely be able to drop the dense fog advisory across our southern tier counties prior to daybreak. Otherwise, in the wake of the cold front, a drier low-level airmass will advect southward into northern IL this morning, bringing an end to the fog and the persistent area of low stratus. However, in spite of this, higher level cloud cover will quickly be on the increase ahead of the next approaching impulse, so another cloudy day is anticipated today, with highs in the upper 40s to around 50.

A sheared mid-level impulse and associated weak surface low will shift eastward across the mid Mississippi Valley through the day. While this will continue to favor an expansive area of rainfall into tonight across parts of the Midwest, there will be a sharp northward gradient in the rainfall setting up across central IL and IN. Accordingly, the prospects of any meaningful rain today into tonight continues to diminish across far northern IL, particularly areas along and north of I-80. We thus continue to confine chance POPs mainly south of the Illinois and Kankakee Rivers later today into this evening.

A period of dry weather, with more sunshine and moderating temperatures is expected for the weekend, owing to an area of surface high pressure shifting across the mid section of the country. However, another upper-level low is expected to eject northeastward out of the Desert Southwest later this weekend. This system will result in our next good threat of widespread rain as it shifts across our region in the Monday afternoon through Tuesday morning time frame. Thereafter, a northern stream impulse is likely to carve out an upper trough over the Great Lakes into the Thanksgiving holiday weekend. For our area this will result in notably colder conditions by Thanksgiving day, with highs only in the 30s.

KJB

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 552 AM CST Fri Nov 21 2025

Main Item of Note:

- North-northeasterly wind shift at MDW and ORD this afternoon.

There are no significant flying concerns through Saturday morning. Though the TAF sites except GYY scattered to VFR CIGs early this morning, can't rule out temporary MVFR CIGs at times this morning. GYY should scatter by midday. MVFR VSBY in BR at RFD, DPA, and GYY should improve by ~14-15z.

At ORD and MDW, light north-northwesterly winds this morning are expected to shift to north-northeasterly (020-050) this afternoon, with some uncertainty in timing. An earlier wind shift is currently favored at MDW vs. ORD, as depicted in the TAFs. While speeds should remain relatively light, can't completely rule out brief near 10 kt speeds observed at runway sensors. Winds should then return to north-northwest this evening through Saturday morning. Some minor VSBY reductions in BR may occur at RFD, DPA, and GYY tonight, though not explicitly indicated in the TAFs.

Castro

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.