FXUS63 KLOT 091741 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1241 PM CDT Thu Jul 9 2026 .KEY MESSAGES... - Scattered thunderstorms are expected at times through this evening. These storms will be capable of locally heavy rainfall which may lead to flooding, particularly if they stall or redevelop over areas hardest hit from last weekend. - The strongest storms will also be capable of gusty to locally damaging wind gusts this afternoon and evening, greatest threat south of I-80. - Mainly dry and warmer weather is expected this weekend into early next week. && .DISCUSSION... Issued at 342 AM CDT Thu Jul 9 2026 The earlier complex of thunderstorms approaching from eastern IA/southwest WI has mostly eroded with only a few areas of rain remaining. Not currently expecting any additional lightning through the remainder of the overnight hours with this activity but will still have to keep an eye on the remnant MCV moving into northwest Illinois but it should move out over the lake already by 7-8 AM. Earlier warm advective showers southwest of the metro managed to produce a few lightning strikes but have since decreased in coverage. Still can't rule out a few spotty showers south of the Kankakee River Valley through daybreak. Attention then turns to a second MCV moving across central Iowa. This feature is expected to progress east toward the area through mid morning. Concerns are that this could lead to an earlier "first round" of isolated to scattered showers and thunderstorm development from mid morning through early afternoon (30-40 percent chance). Forecast soundings show a largely uncapped environment here locally already after 9-10 AM so any forcing for ascent (such as with an MCV) would support thunderstorm development. Model guidance has been struggling with handling these smaller scale mesoscale features and have based the first 12 hours of the forecast largely on radar, satellite, and observational trends. As the aforementioned MCV begins to shift southeast out of the area toward mid-late afternoon, additional thunderstorm development may then occur within the vicinity of a residual outflow boundary or convergence axis situated across northern and northeast Illinois. Exactly where this boundary ends up as well as what the coverage of showers/storms will be remains lower confidence, at least initially given a potentially slower arrival of the parent mid-level vort/wave (which is still out over northern NE/southern SD). Suspect that coverage may remain more isolated to widely scattered during the afternoon until the wave arrives leading to increasing coverage during the evening (potentially still over portions of the Chicago metro) before gradually shifting south and east and out of the area overnight. The primary hazard with any thunderstorms today (from mid morning through this evening) will be localized heavy rainfall. PWATs in the upper end of climatology (2"+) will be supportive of instantaneous rainfall rates in excess of 1-2"/hr. Given the increased susceptibility for flooding in many areas after last weekend's multiple rounds of heavy rainfall, will continue to message the localized threat of flooding. In spite of generally weaker shear, precip loaded downbursts will remain possible with the strongest storms which could produce strong to locally damaging wind gusts (40-60 mph). The greatest threat (and level 1 out of 5 threat for severe weather) is greatest for areas well south of I-80 but can't fully rule it out areawide. In the wake of our showers and storms a backdoor cold front is expected to move inland off Lake Michigan late in the evening. This may bring a period of fog and/or very low clouds across much of the metro through early Friday morning, some of whichcould end up locally dense. Something to keep an eye on with later forecasts. Looking ahead to Friday, additional convectively augmented shortwaves are expected to move across the Mid-Mississippi and Ohio Valley regions. Think that the majority of the shower and storm coverage with these features will remain largely south of the area but have maintained 20-40% chances for areas south of a Peru, IL to Rensselaer, IN line in case they end up a bit farther north. While a few diurnally driven showers can't be ruled out on Saturday, upper level ridging expands across the central CONUS over the weekend into early next week which should lead to mainly dry conditions into the first part of next week with temperatures in the upper 80s to around 90. Given we will be on the northeast periphery of the ridge we will have to monitor the potential for thunderstorm complexes rounding the ridge across the broader region toward midweek. Petr && .AVIATION /18Z TAFS THROUGH 00Z SATURDAY/... Issued at 1241 PM CDT Thu Jul 9 2026 Aviation forecast concerns for the 18Z TAFs: - Scattered convective SHRA/isolated TSRA likely across terminals especially late afternoon into early/mid evening. IFR/low-MVFR vis possible in brief heavy rain. - MVFR ceilings develop late tonight with a period of IFR possible toward daybreak. Fog also possible from Chicago Lake Michigan shore west/northwest with MVFR/IFR vis possible. Improvement to VFR expected around midday Friday. - Weak cold frontal passage this evening will shift winds to the N/NE. NE winds persist through Friday. A weak mid-level circulation (remnant MCV from overnight convection to our west) was tracking east across northern IL at midday, atop a moist low-level air mass ahead of a weak, slowly- approaching cold front. Scattered showers have been percolating near and ahead of the weak MCV, though extensive cloud cover and weak lapse rates have limited the depth of this convection and no lightning has been observed near the terminals at this time. Shower and eventually isolated thunderstorm coverage is expected to increase somewhat during the mid-late afternoon hours however, as a low-amplitude mid-level wave and the weak cold front approach during our peak diurnal warmth. Thus the greatest TSRA potential for the terminals looks to be from late this afternoon into early this evening, though coverage will likely remain only widely scattered. Have trimmed TS mention to VC/PROB30 based on these expectations. Scattered SHRA may persist into the overnight hours, as the weak cold front eventually moves slowly through the area. Modest west-southwest winds are expected to turn north-northeasterly behind the front overnight, and remain north-northeast through the day Friday. High-res guidance continues to support fairly extensive MVFR ceilings after midnight behind the front, which may linger as late as midday Friday. Guidance also indicates the potential for a period of IFR ceilings and MVFR/IFR fog from the IL Lake Michigan shore north and west during the predawn hours, and have included a tempo mention for this. While visibility should improve a few hours after sunrise, ceiling improvement to VFR may not occur until midday. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago