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Skokie, Illinois Weather Forecast Discussion

839
FXUS63 KLOT 212339
AFDLOT

Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 639 PM CDT Sun Sep 21 2025

.KEY MESSAGES...

- While there will be many dry hours, the threat of periodic showers and thunderstorms will continue through at least the first half of the upcoming work week.

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.DISCUSSION... Issued at 252 PM CDT Sun Sep 21 2025

Through Monday:

Broader, synoptic scale trough will slowly move east across the upper Mississippi Valley into the upper Great Lakes through Monday. Multiple smaller scale vorts, that tend to be not particularly well resolved by numerical guidance, will continue to pivot around the base of the larger trough and lead to more focused areas of shower and thunderstorm development.

Areas of scattered showers and isolated thunderstorms ongoing this afternoon seem to be driven by a couple of different waves, one favoring our southern CWA and the other our northern and northwestern CWA. The "gap" from Chicago to northern LaSalle County could still fill in later this afternoon as the vorts move eastward, probably aided by some enhanced convergence from collapsing thunderstorm outflow.

The afternoon activity is likely to decrease in coverage and intensity after sunset, however can`t rule out some isolated activity lingering into the mid-late evening. Attention later tonight will turn west toward a slightly more formidable shortwave currently over northwest MO. Given the projected path of this wave, our southern CWA and even more so south of our CWA should be the favored area for showers and perhaps some isolated thunderstorms later tonight into Monday morning.

That shortwave should push east of our area Monday morning, likely bringing an end to any organized shower/isolated storm threat. Our area will remain on the southern end of the circulation associated with the broader synoptic trough. With just some modest heating, atmosphere will likely become unstable and uncapped again Monday afternoon. Any smaller scale vort pivoting around the cyclonic flow on the southern flanks of the trough could lead to another round of scattered showers and perhaps some isolated thunderstorms Monday afternoon.

- Izzi

Monday Night through Sunday:

The regional synoptic pattern will remain largely unsettled this week as a series of impulses are progged to traverse the Midwest, all while maintaining sufficient moisture to support frequent chances for rain. The forecast in the long term picks up late Monday when we`ll find an upper low scooting across the upper Midwest. Deep layer moisture on the leeward side of the trough will get shunted to our east during the night as the trough axis moves across the CWA. This should focus the highest rain and continued low thunder chances into our southern and eastern CWA for the evening and night, but ample ingredients will remain for possible scattered showers area-wide. Aside from a departing 250mb jet max and transient vort lobes around the perimeter of the upper low, an overall lack of deep forcing may generally dampen rain coverage and thunder potential, especially during the overnight period as parcels through the lowest couple of hundred millibars should be well-capped.

There remains rather low confidence in precip trends and thunderstorm potential next week, but intermittent bouts of rain will be possible each day into the weekend. Another feed of deep moisture will fill in during the day on Tuesday ahead of a secondary trough axis pivoting through the Midwest providing additional rain and low thunder chances. Medium range guidance is hinting at another vertically-stacked upper low spinning up over the Midwest during the middle of next week. The GFS tracks this feature and its surface response right across the CWA while the Euro is a bit displaced to the east. Regardless, we have additional rain and storm chances in the forecast associated with this feature through the latter half of the week. High pressure will build in behind the low. If the Euro is correct, the high would propagate into our area as early as Thursday night and conditions should look quiet for Friday. If the GFS is correct and the low takes it time departing the region, then expect better chances for precip on Friday. Once that high does settle in by this weekend though, conditions should be largely rain-free into the early part of next week.

Doom

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.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/... Issued at 639 PM CDT Sun Sep 21 2025

Main Concerns:

- TS nearby as of this writing bringing varying wind directions and speeds at the Chicago metro terminals

- MVFR BR possible outside of Chicago overnight

- Potential for scattered SHRA and maybe isolated TS overnight into early Monday, mainly at the Chicago metro terminals

A thunderstorm passed just north of ORD as of this writing, with outflow effects resulting in temporary brisk northerly winds. MDW should see a temporary wind shift to northerly during the 00-01z hour from another outflow boundary sagging south. Aside from a few storms north of ORD and a cluster of storms in northwest IN to the southeast of GYY, other widely scattered convection is struggling. Plan to update to remove VCTS in the Chicago metro TAFs as soon as CB cores fully dissipate.

We`ll need to keep an eye on the possible development of light fog and associated VSBY reductions outside of Chicago later tonight. Another round of showers, perhaps accompanied by isolated embedded thunderstorms, may occur overnight into early Monday, though confidence is low (PROB30s maintained). Isolated SHRA/TS are also possible Monday afternoon, with the probability of occurrence and confidence too low for inclusion in the TAFs. Expect southwest to south-southwest winds on Monday with speeds primarily below 10 kt.

Castro

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.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None.

&&

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NWS LOT Office Area Forecast Discussion

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