


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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940 FXUS63 KLOT 271901 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 201 PM CDT Fri Jun 27 2025 .KEY MESSAGES... - Chance of thunderstorms this evening southeast of I-55. - After a bit of a reprieve from heat and humidity Saturday (especially near the lake), another hot and humid day is expected Sunday. - Additional threats for mainly afternoon/evening storms Sunday and Monday. && .DISCUSSION... Issued at 201 PM CDT Fri Jun 27 2025 Through Saturday Night: This morning`s thunderstorms are moving eastward out of the forecast area into Indiana. Meanwhile, a cold front is currently descending southeastward across the forecast area, which shows up fairly clearly on visible satellite imagery. As the area destabilizes this afternoon, there is a chance that an additional round of showers and storms can form along the front, likely southeast of Interstate 55. Given the moist air mass with dew points over 70 across the area, localized downpours are possible over areas that already saw some rain earlier today. Shear profiles do not look particularly exciting, although recent SPC mesoanalysis has around 500-1000 J/kg of DCAPE. Strongest storms could potentially have localized stronger wind gusts, mainly southeast of Interstate 57. However, the front is expected to continue its movement east through the afternoon so any shower and storm threat should diminish quickly as it exits this evening. Surface high pressure will build into the area overnight and into Saturday. Dewpoints will drop back into the 60s (finally!) with high temperatures tomorrow the mid to upper 80s. A lake breeze is expected to develop in the morning which will help keep the lake shore in the mid 70s. Subsidence and drier air mass should keep things dry through Saturday. Attention will turn to northern Iowa and southern Minnesota late Saturday afternoon and evening. High res guidance is suggesting a potential MCS could develop and move southeastward. However, there is fairly decent consensus that it weakens as it crosses the Mississippi River during the night. Perhaps it could produce a stronger outflow that makes its way down to northern Illinois in the early hours of Sunday morning, but confidence is low. For now, a dry forecast remains through Sunday morning with overnight low temperatures in the upper 60s and lower 70s. DK Sunday through Friday: As surface high moves off to the east Sunday, southerly winds will send the hot and humid air mass back northward into our area. Given the progged sfc gradient from the due south, there could be a weak afternoon lake breeze along the Illinois north shore Sunday afternoon, otherwise look for highs mostly near or in the lower 90s. Dewpoints rising back into the low-mid 70s are expected to push heat indices back up to around 100 degrees. Forecast soundings Sunday afternoon show the atmosphere moderately to strongly unstable with little if any cap left during the afternoon. Strongest synoptic forcing should remain well north/west of our CWA during the day Sunday, however guidance suggests the TUTT cell (tropical upper tropospheric trough) over the southeastern United States will drift northwestward potentially getting close enough to our CWA to bring the smattering of scattered afternoon/evening convection north into portions of our CWA Sunday afternoon and evening. At least periodic chances of showers and thunderstorms will continue Sunday night into Monday as an upper trough digs into the upper Mississippi Valley and Great Lakes. Still a little early for specifics, but highest chances look to be Monday afternoon/early evening as cold front moves across the area. Upper trough sets up over the Great Lakes Tuesday and Wednesday with associated Canadian high pressure ushering in a much less humid air mass and more seasonable temperatures (80s). Medium range guidance suggests that the upper trough will be replaced by upper ridge that gradually builds eastward into the region later next week. An eventual return to warmer and more humid conditions is expected late in the week along with shower and thunderstorms chances. - Izzi && .AVIATION /18Z TAFS THROUGH 00Z SUNDAY/... Issued at 1221 PM CDT Fri Jun 27 2025 Period of some MVFR CIGS expected during the early-mid afternoon before CIGS likely scatter out and lift later this afternoon. Otherwise, with showers and thunderstorms likely to remain well south and east of the terminals, look for VFR conditions through the remainder of the TAF cycle. Gusty westerly winds today will diminish this evening and become light and variable tonight into Saturday morning. Winds will become light easterly Saturday morning with a lake breeze likely to result in a modest bump up in the winds to around 10kt at ORD and MDW Saturday afternoon - Izzi && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago