FXUS63 KLOT 090842 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 342 AM 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 /06Z TAFS THROUGH 12Z FRIDAY/... Issued at 100 AM CDT Thu Jul 9 2026 Forecast concerns for the terminals... - 20-30% chance for isolated showers early Thursday morning, mainly near RFD. - Scattered showers and thunderstorms expected Thursday afternoon and evening. Any of which could result in localized heavy downpours and reduced visibility. - MVFR ceilings Thursday night into Friday morning with potential for patchy fog after midnight. A busy weather and complicated TAF period ahead as several disturbances will be pivoting through northern IL and northwest IN. Prior to the arrival of the disturbances, increasing VFR clouds are expected tonight with light southwest winds that will become more westerly by Thursday morning. As we head into Thursday morning, the line of decaying line of showers and embedded thunderstorms (currently in IA and southwest WI) will be moving through northwest IL. With radar continuing to show these showers eroding suspect that mostly dry conditions will prevail through Thursday morning, but with an embedded convectively enhanced low being noted within the showers cannot fully rule out some isolated showers developing around daybreak and lingering through the morning (20-30% chance). Due to the lower confidence on coverage of any morning activity have opted to maintain VCSH at all TAFs with a PROB30 at RFD where confidence is slightly higher that something could materialize. Regardless of what develops Thursday morning, scattered showers and thunderstorms are expected to develop along the outflow boundary from tonight's storms that should be draped over northern IL. While exact timing as to when the afternoon activity will kick off remains uncertain, latest forecast guidance trends seem to be leaning towards a 21-22z initiation with thunderstorms likely to persist through at least 01-02z as the boundary slowly drifts south through the terminals. Though, there is a chance that some showers could linger through the evening especially if the boundary is slower than forecast. For now have opted to maintain the broad VCSH mentions with targeted PROB30s for the better thunder windows at each location. Any showers/storms this afternoon will be capable of producing locally heavy downpours which would result in IFR visibilities and possibly even some ponding issues particularly near the saturated areas from last week's rains. Showers and storms should taper after 03z as the boundary drifts south and the associated disturbance pivots east of the area. In the wake of the boundary a northeast wind shift will occur with speeds initially around 8-10 kts but those will be waning to around 5 kts after midnight. Ceilings will also lower to MVFR behind the boundary where they look to remain for the rest of the forecast period. While there is a signal for some IFR ceilings as well, confidence on their coverage is low so have opted to handle with a SCT012 mention for now. Furthermore, there is also a decent signal for patchy fog to develop near Lake Michigan and ooze inland overnight some of which could be locally dense. At this time the 30-hour TAFs will have a 6SM BR mention to tease the fog, but more refined TEMPOs may be needed for lower visibilities as confidence grows. Yack && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago