textproduct: Chicago

KEY MESSAGES

- Periods of showers and/or drizzle are expected at times through the weekend, though the highest chances/coverage is expected tonight into Saturday morning.

- Additional periods of wet weather are likely next week.

DISCUSSION

Issued at 100 PM CDT Fri Oct 30 2026

There is a mid-level trough over west central Texas (via SPC Mesoanalysis) that is expected to gradually move northeastward over the southern Plains today/tonight. Additionally, a stout 100+ knot upper jet is located over southeastern Ontario, placing northern Illinois in the right entrance region of its location and therefore in an area increased upper level divergence. For know, a near surface dry airmass has been winning the day keeping all activity on KLOT radar currently showing up in the western portions of the forecast area to mainly virga, to maybe a few sprinkles. As a plume of increased moisture and warm air advection moves into the area this evening and in the overnight, there is a better chance for increased coverage for light showers into Saturday morning. Given the unfavorable time of day, thunder is not expected. Although slightly steepening low/mid-level lapse rates keeps the chances non- zero, but below formal forecast mention.

As the upper level jet streak weakens and moves east tomorrow morning, the mid/upper level trough is expected to move over the western Great Lakes Saturday afternoon and evening. With weaker forcing and a lingering dry boundary layer air mass, confidence is lower for precipitation tomorrow evening. Slight chance PoPs were maintained for tomorrow night for the isolated chance for a light shower, if not just sprinkles/drizzle during any trick-or-treating. Certainly not any kind of washout, some areas will probably remain completely dry. But enough of a nuisance to keep precip mention in the forecast through Sunday morning.

A pseudo-stationary upper level cutoff low west of Seattle, WA is projected to finally move eastward over the intermountain west on Sunday as another short wave currently near Baja California moves northward, merging with the low, further amplifying the trough early next week. While specific details still need to be ironed out, models are showing fairly good agreement that this trough will induce surface cyclogenesis east of the Rockies and that will move over the Great Lakes in the middle of next week bringing better chances for widespread rain. Behind this system, a cooler airmass will drop temperatures down to make it feel a little more autumn-like.

DK

AVIATION /18Z TAFS THROUGH 00Z SUNDAY/

Issued at 1213 PM CDT Fri Oct 30 2026

- Potential for sprinkles this afternoon (chances around 30-40 percent).

- Additional intermittent periods of primarily light showers developing late tonight through Saturday.

- East to southeasterly winds expected through the TAF period.

A period of sprinkles remains possible this afternoon. Have introduced some PROB30 mentions to account for this. This evening and overnight, additional light showers are expected to develop. A few embedded waves of steadier rainfall, perhaps with MVFR cigs/vsbys, may develop, but uncertainty regarding specific timing and placement remains high enough to warrant simply maintaining PROB30 groups at this time. Intermittent sprinkles will likely continue through Saturday afternoon. East to southeasterly winds around 5-10 kts will prevail through the TAF period.

Carlaw

LOT WATCHES/WARNINGS/ADVISORIES

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