textproduct: Chicago

KEY MESSAGES

- Widespread showers will gradually diminish in coverage late this afternoon. Pockets of light showers/drizzle may continue at times tonight into Monday morning.

- Below normal temperatures through the end of the week.

DISCUSSION

Issued at 1230 PM CDT Sun Sep 20 2026

A mid-level shortwave/convectively augmented MCV continues to shift east directly overhead early this afternoon. At the surface, a synoptic cold front is pushing southward, with gusty northeasterly winds developing in its wake. As this MCV/mid- level wave presses eastward, the greatest coverage of steady showers will gradually push east into Indiana through late this afternoon. The lightning threat has ended for locales north of I-80, as the main elevated instability axis continues to move southward. Can't rule out a few bonafide thunderstorms developing across our far south (Ford - Benton counties) this afternoon along the cold front. Forecast effective inflow layers are very shallow, greatly limiting available SRH, but deep layer shear values near 35 kts could potentially support a few mini supercells. The window for this will be very brief, perhaps 3-6 PM (if that), with the main potential focusing east and south of our forecast area.

Since low-level moisture won't really go anywhere tonight, pockets of light showers/drizzle will be possible into Monday morning as additional vorticity maxima meander overhead. Cloud bases may lift sufficiently Monday afternoon to bring an end to lingering precipitation, but additional disturbances drifting atop the frontal zone may result in sporadic sprinkles/light precip chances into Tuesday. Persistent strong northeasterly winds will result in a prolonged period of dangerous swimming conditions at area beaches due to high waves and strong currents.

Thereafter, we'll get a notable injection of drier air from the east as high pressure settles across the Upper Midwest and Great Lakes region through the mid and end of the week. Seasonably cool and pleasant conditions look to prevail during this period, with high temperatures generally in the 60s with a very modest warming trend into week's end. Upper-level blocking looks like it'll hold most precipitation chances to a minimum, at least until next weekend when a small signal for precipitation chances may return.

Carlaw

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1230 PM CDT Sun Sep 20 2026

Forecast concerns for the terminals...

- Lingering showers and drizzle through early evening, showers may result in brief visibility reductions.

- IFR ceilings this afternoon to gradually lift towards MVFR this evening and overnight. VFR conditions not expected to return until Monday afternoon at the earliest.

- Breezy northeast winds gusting 20-25 kts through the TAF period.

Bands of rain showers and drizzle continue to pivot around a convective surface low in northwest IL. These showers/drizzle are expected to persist through early evening before precipitation eases. However, there is a growing concern that some lingering low-level moisture in the presence of weak ascent may continue to develop instances of drizzle through Monday morning. Since confidence on drizzle coverage is low have opted to maintain a dry forecast after 03z, but did add a FEW009 mention to the TAFs to tease the potential for drizzle.

Regardless, IFR ceilings are expected to persist through early evening before gradually lifting to MVFR overnight pending any of the aforementioned drizzle. MVFR ceilings are forecast to persist through much of Monday morning before skies attempt to lift to VFR Monday afternoon. Though, confidence on when VFR conditions return is low at this time. Otherwise, expect breezy northeast winds to prevail through the TAF period with gusts generally in the 20-25 kt range.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...Beach Hazards Statement through Tuesday evening for ILZ006- ILZ103-ILZ104.

Flood Watch until 1 PM CDT this afternoon for ILZ008-ILZ010- ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ103- ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Beach Hazards Statement through Tuesday evening for INZ001.

Flood Watch until 1 PM CDT this afternoon for INZ001-INZ002.

Beach Hazards Statement through Monday morning for INZ002.

LM...Small Craft Advisory until 7 PM CDT Tuesday for Winthrop Harbor IL to Burns Harbor IN.

Small Craft Advisory until 7 AM CDT Monday for Burns Harbor to Michigan City IN.