FXUS63 KLOT 150558 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1258 AM CDT Thu Oct 15 2026 .KEY MESSAGES... - A fall storm system will move through the area Thursday and Friday, bringing periods of rain showers and gusty northwesterly winds (the latter primarily on Friday). - Frosty and near-freezing conditions are favored away from Lake Michigan Friday night into Saturday. - After the brief period of chilly weather, there will be a warming trend this weekend into early next week. && .DISCUSSION... Issued at 310 PM CDT Wed Oct 14 2026 Through Thursday night: Other than a few spits of drizzle near Lake Michigan, most of the area has since dried out from the overnight and early morning showers and thunderstorms. The combination of overcast skies and persistent onshore northeasterly winds have held temperatures in the low to mid 60s near/north of I-80. Farther south, a thinning of the stratus layer with occasional peeks of sunshine has allowed temperatures to warm into the upper 60s and lower 70s. Generally expect the cloud cover to fill back in through this evening and overnight with temperatures only dropping into the 50s. A fall storm system remains on track to lift across the region on Thursday which will bring widespread showers and a few rumbles of thunder to the area. The greatest shower coverage is currently favored late morning through the afternoon. Hi-res guidance continues to depict a relative minimum in precipitation developing on the southwest side of the surface low during the late afternoon and early evening. Depending on how far north the low tracks, increasing instability southeast of this dry wedge may lift into the far southern forecast area, south of a Pontiac to Rensselaer line. While the better instability remains farther south into central and southern Illinois, an isolated stronger storm can't be ruled out. Any more robust showers and embedded thunderstorms will be capable of efficient rainfall rates for this time of year in the presence of PWATs potentially upwards of 1.5-2". The limited coverage of stronger showers/storms should keep any flooding potential tied mainly to ponding on roadways and poor drainage spots. Friday: In the wake of the departing storm system and associated strong cold front, the surface pressure gradient increases markedly across the area on Friday. This will lead to blustery northwest winds gusting up to 30-40+ mph, highest along the northwest Indiana lakeshore. In addition, model guidance has trended slightly more saturated within the low-cloud layer which may support the redevelopment of gusty diurnal showers. Weak instability within the layer and colder cloud tops may support some graupel as well. Temperatures on Friday will likely struggle to warm out of the low to mid 50s, making for the coldest day of the season so far. As the northwesterly winds begin to turn more northerly over Lake Michigan, a broken band (or bands) of lake effect rain showers will focus into northwest Indiana late Friday afternoon through the evening. Waves are also expected to increase and may lead to minor lakeshore flooding or erosion, particularly along the Porter County shore. Friday night onward: Skies will quickly clear out after midnight Friday, which will allow for efficient radiational cooling amidst an already cooler airmass. This will likely lead to areas of frost development outside of Chicago and away from Lake Michigan, coverage dependent upon how light winds end up. Can't rule out temperatures in portions of interior northern Illinois dropping into the lower 30s. However, confidence is not high enough for a freeze watch with this update. While still cooler on Saturday with temperatures in the 50s to around 60, a return of southwesterly low-level flow will begin a gradual warming trend that continues through early next week, bringing a return to above normal temperatures. Petr && .AVIATION /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 1258 AM CDT Thu Oct 15 2026 Forecast concerns for the terminals... - VFR to high end MVFR ceilings tonight. - Storm system will arrive Thursday morning and bring periods of showers and IFR conditions, at times LIFR, through Thursday evening. - Improving ceilings Thursday night with increasing northwest winds gusting 20-25 kts. A busy TAF period weather wise is ahead as the developing storm system in the southern Plains will be moving into and through the Great Lakes Thursday morning through Thursday evening. Prior to the system's arrival, expect VFR to high end MVFR (2500-4000 ft) ceilings to persist off and on through tonight with easterly winds around 8-10 kts. While a few warm advection showers may develop as early as 09-10z tonight, it seems the bulk of the rain showers will hold off until mid to late morning Thursday as the core of the aforementioned storm system arrives. Once the rain showers arrive they will persist in an off and on capacity through Thursday evening resulting in MVFR visibilities and IFR ceilings. That said, with the surface low forecast to traverse directly overhead confidence continues to grow in a period of drizzle and LIFR conditions for a few hours late Thursday afternoon through early Thursday evening. Given that there is still some uncertainty as to the duration of the drizzle and LIFR conditions have opted to maintain PROB30s for this potential for now. Additionally, there is also a low end chance (10-15%) for an isolated rumble or two of thunder near and south of I-80 (mainly effecting GYY) between 21z-01z as a plume of instability oozes northward but confidence remains too low for any formal TAF mention. Rain is expected to gradually taper from west to east around and after midnight Thursday night. Ceilings will also improve as the rain ends with MVFR conditions expected to return around midnight and persist through the rest of the TAF period. As for winds, directions will become more southeasterly Thursday morning as the system arrives before becoming light and somewhat variable as the surface low passes overhead. Though, directions beneath the low should generally favor a south-southeast direction (170-180 degrees). In the wake of the system's cold front wind directions will turn west-southwest and then finally northwesterly around midnight Thursday night. Speeds will also be increasing in the wake of the cold front with gusts peaking around 20-25 kts Thursday night, though some locally higher gusts may be seen if deeper mixing is achieved. These gusty northwest winds will prevail through the day on Friday as well. Yack && .MARINE... Issued at 310 PM CDT Wed Oct 14 2026 Strong northwesterly gales to 40 kt and very hazardous waves are forecast to develop Friday afternoon in the wake of a departing fall storm system, becoming more northerly into Friday evening. Accordingly, a Gale Watch has been issued for the Illinois and northwest Indiana nearshore waters from 1 PM Friday through 1 AM Saturday. Increasing lake induced instability will become supportive of the development of a band of lake effect showers over Lake Michigan Friday afternoon and evening. Waterspouts also cannot be ruled out within the strongest showers. Petr && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory until 3 PM CDT this afternoon for Winthrop Harbor to Wilmette Harbor IL. Gale Watch from Friday afternoon through late Friday night for the IL and IN nearshore waters. Small Craft Advisory until 10 AM CDT this morningfor Wilmette Harbor to Northerly Is. IL. Small Craft Advisory until 4 AM CDT early this morning for Northerly Is. IL to Michigan City IN. && $$ Visit us at weather.gov/chicago