FXUS63 KLOT 200557 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1257 AM CDT Wed Aug 20 2025 .KEY MESSAGES... - Dangerous swimming conditions expected at southern Lake Michigan beaches today through early Thursday. - A chance for sprinkles or very light showers tonight into Wednesday morning. - Patchy fog possible tonight into early Wednesday. - Temperatures early to mid next week will likely be an early Fall preview! && .DISCUSSION... Issued at 246 PM CDT Tue Aug 19 2025 Conditions are quiet and rather comfortable out there this afternoon. The cold front that moved across late last night driving heavy showers and thunderstorms has since pushed away from our CWA into central IL. Advecting in behind this front and overspreading the area is a thick stratocumulus deck. The cold advection and cloudy skies have kept temperatures largely in the 70s so far with only a couple of sites in our south reporting 80 as of 2 PM. Waves are building on southern Lake Michigan this afternoon as gusty northerly winds move over the water. The Michigan City buoy is already reporting wave heights greater than three feet and they're climbing quickly, with a beach hazards statement in effect for our Indiana counties. The high swim risk will take hold of Illinois beaches this evening. Then expect dangerous swimming conditions to persist through tomorrow and stretch into at least Thursday morning. A very subtle low level wave/baroclinic zone will be pushing south across the region this evening into tomorrow. A number of model camps are resolving southward-moving pockets of very light rain or sprinkles overnight while the wave moves across, mostly over areas near the lake. Boundary layer moisture will stretch farther inland during the morning spreading light precip chances west of the Chicago metro for the morning hours. As inversion heights lift, the shallow unstable layer may become supportive of true light showers for a period during the morning before drier air advects in for the afternoon. Additionally, there is a good-looking signal for areas of fog to develop overnight with patches of dense fog even possible. This is primarily a concern across the outlying suburbs and outside of the Chicago metro. How much clearing skies see tonight will also play a role in the fog potential, but that's rather uncertain. A large upper high will park itself over the Four Corners region for the back half of this week and spread a quiet upper flow regime over the Midwest. This should bring dry and largely sunny conditions to Thursday and Friday. Temperatures leading up to this weekend should be seasonably warm in the upper 70s and low 80s. A cold front looks to move across the region Friday night and Saturday, but a lack of forcing and instability could keep precip coverage rather low. High pressure should then build in behind the front and keep conditions dry for Sunday. Temperatures are expected to fall to the cooler side of average early next week behind that cold front. Doom && .AVIATION /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 1257 AM CDT Wed Aug 20 2025 Only Items of Note: - Potential for IFR VSBY in BR/fog at RFD early this morning. - MVFR CIGs developing in the pre-dawn hours today and persisting through early to mid afternoon near the lake. The theme of much quieter flying conditions will continue through the next several TAF cycles. In the near term of the current TAF period, patchy dense fog has developed at RPJ where skies were mostly clear. There may be enough clouds to prevent LIFR VSBY at RFD, though a period of at least occasional IFR VSBY appears likely enough to maintain TEMPO mention. For DPA, the more likely scenario looks to be TEMPO MVFR VSBY. MVFR CIGs will stream south in the pre-dawn through mid morning hours, with lake influence keeping them in place a bit longer at the near-lake terminals. North-northeast winds will gust to near/around 20 kt at times from this morning through the mid- late evening, followed by prevailing 5-10 kt speeds thereafter. Castro && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Beach Hazards Statement through Thursday morning for ILZ006- ILZ103-ILZ104. IN...Beach Hazards Statement through Thursday morning for INZ001- INZ002. LM...Small Craft Advisory until 4 AM CDT Thursday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago