615 FXUS63 KLOT 132323 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 623 PM CDT Wed Aug 13 2025 .KEY MESSAGES... - Uncomfortable heat and humidity returns this weekend with heat indices 95 to 105 degrees. - Shower and storm chances return on Sunday and continue early next week. && .DISCUSSION... Issued at 249 PM CDT Wed Aug 13 2025 Expect primarily dry weather for the remainder of the day, with only a small chance (15%) for an isolated sprinkle or two in the vicinity of the lake breeze boundary. This small threat will end quickly with sunset this evening as the boundary layer quickly cools and stabilizes. Light winds and mainly clear skies will allow temperatures to drop back through the 60s tonight, with even a few mid to upper 50s possible in the typical cool spots by early Thursday morning. Lingering low-level moisture may again foster some patchy fog development towards daybreak, particularly across interior sections of northern IL, back into and central IL and IN. Quiet and dry weather will persist through the remainder of the week as upper-level ridging begins to build back over the Midwest into the western Great Lakes. The main weather story with this pattern will be the quick return to hot and increasingly humid conditions Friday, and especially on Saturday. Temperatures will be warming back to around 90 on Friday, then into the low to mid 90s on Saturday. These temperatures, in combination with increasing humidity will yield heat indices into the mid to upper 90s Friday afternoon, and likely to 100 to 105 by Saturday afternoon. These hot and humid conditions look to persist on Sunday. However, attention will be focused on the evolution of a cold front shifting southward into the Upper Midwest and Upper Great Lakes Saturday into early Sunday. With this front likely to become a focus for strong convection to our north through the weekend, waves of enhanced storm outflow may act to drive the effective cold front far enough south to briefly enter northern parts of our area as early as Sunday afternoon. Confidence on this occurring remains low at this time. However, if this occurs some heat relief would be possible along with an increased threat of storms Sunday afternoon. The threat of storms will continue early next week (Monday and Tuesday), though the best chances will likely be tied to the timing of another cold frontal passage associated with an area of low pressure expected to track through the Upper Midwest. Due to continued uncertainty in the finer scale details, we made no changes to the NBM output, which generally broad brushes 20-30% chances for storms both days. Conditions are also likely to remain very warm and humid for a period early next week, though there are signs that cooler weather will shift into the area behind this next cold front for the second half of next week. KJB && .AVIATION /00Z TAFS THROUGH 06Z THURSDAY/... Issued at 623 PM CDT Wed Aug 13 2025 Only forecast concern is fog potential overnight/Thursday morning outside the Chicago terminals. A lake breeze will continuing move west until it dissipates with sunset this evening. Winds will become light and variable for much of the area tonight. Where directions persist, they will likely be light north/northwest. Winds will become northeast Thursday morning and then more easterly with a lake breeze for the Chicago terminals Thursday afternoon. Further inland, winds may trend more southeasterly. Patchy fog is expected overnight into early Thursday morning, mainly south and west of the Chicago terminals. Confidence is low for how widespread the fog may become. For now have included mvfr tempo mention at only RFD. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago