


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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935 FXUS63 KLOT 141100 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 600 AM CDT Mon Jul 14 2025 .KEY MESSAGES... - Humidity along with periodic thunderstorm chances return Tuesday through Thursday, with some threat for localized flash flooding and severe weather late Wednesday through Thursday. - After a brief break Friday, humidity and the chance for occasional bouts of storms expected to return next weekend, though the weekend doesn`t look to be a washout. && .DISCUSSION... Issued at 308 AM CDT Mon Jul 14 2025 High pressure over northern Illinois early this morning has brought with it some lower dewpoints into the area, though the higher dewpoints are lurking to the south as close as central Illinois. Light winds and the recent rains have allowed for patchy dense fog to form well south of I-80 within that more humid air mass. The patchy dense fog will quickly dissipate after sunrise. Otherwise, look for a good deal of sunshine and seasonably warm temperatures today. Light winds will allow for an afternoon lake breeze with slightly cooler temps adjacent to the lake. The HRRR smoke model shows decreasing smoke column integrated smoke concentrations today, so not anticipating smoke to be a significant factor today. A mid-upper level shear axis, the remnants of an upper low and upper trough, from the Red River Valley northeast into the Ozarks today is progged to move northeast into Illinois Tuesday. As it does, light southerly flow will begin to draw the higher dewpoints downstate northward into our CWA. This shear axis was the focus for isolated-widely scattered thunderstorms Sunday afternoon and is expected to continue to do today across the Ozarks, with isolated afternoon convection likely to develop northeast across Illinois Tuesday afternoon. Greatest coverage Tuesday afternoon should be across our southern CWA, though some chances will exist north across the CWA. It looks like we`ll be on the north side of this shear axis, so any storms that do form will likely be moving slowly toward the west! This shear axis is progged to move away from the area Tuesday night into Wednesday, but a very warm, humid, moderately unstable, and nearly uncapped air mass should be in place Wednesday. While the stronger synoptic forcing should remain to our north, closer to the main belt of westerlies, we will need to watch for any MCVs riding east along the southern flanks of the mid level westerlies. Precise timing/track of MCVs this far out isn`t possible, but MCV that does affect the area Wednesday or Wednesday night will have ample moisture and moderate instability to work with, so the threat would exist for locally heavy rainfall and perhaps a localized flash flood threat. In addition, strong to severe storms could be a threat, particularly where any MCV augments the low-mid level flow resulting in more favorable shear profiles. Synoptic upper trough is progged to move across the area Thursday along with the attendant surface front. Prior convection could easily end up modulating where the highest convective chances are Thursday, but the general idea of increasing shower and thunderstorm chances Thursday looks reasonable. Any MCV augmented shear could lead to a corridor with a greater threat for severe weather, especially damaging winds, somewhere in the region Thursday, but where will certainly need to be refined in coming days. Non-convectively disturbed air mass in advance of the front will be very moist leading to thunderstorms capable of producing torrential downpours and a continued localized flash flood threat where storms do occur Thursday. Temperatures Tuesday through Thursday look to be very warm to potentially rather hot depending on coverage of storms and/or possible convective debris. With some sunshine during peak heating, temperatures should get close to, if not into, the lower 90s, which when combined with dewpoints in the low to mid 70s would result in peak heat indices nearing 100 degrees. Any of these days that feature more convective debris or convection during peak heating will probably see highs more in the mid to upper 80s with still very humid conditions and heat indices well into the 90s. Behind the front, Friday looks to be a bit cooler and noticeably less humid with generally dry conditions expected. Will need to watch for the potential for increased beach hazards for Lake Michigan beaches Thursday night into Friday if guidance depicting the stronger northerly flow in the wake of the front pan out. Next weekend, it looks like the front could try and work its way back northward, but the eventual positioning of the front will probably be affected by convection. We look to be on the fringe of the stronger belt of mid-upper level westerlies and certainly within a broad general that could be affected by an MCS or two next weekend into early next. The chance pops offered up by the NBM reflect this threat quite well at this distance. - Izzi && .AVIATION /12Z TAFS THROUGH 18Z TUESDAY/... Issued at 600 AM CDT Mon Jul 14 2025 Could see some high end MVFR VSBY in HZ/FU today, especially this morning at ORD/MDW/GYY, otherwise VFR conditions are expected through the TAF cycle. Winds should remain less than 10kt, even behind a lake breeze which should move through ORD, MDW, and GYY later today with a wind shift to easterly. - Izzi && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Dense Fog Advisory until 9 AM CDT this morning for ILZ032- ILZ033-ILZ039. IN...Dense Fog Advisory until 9 AM CDT /10 AM EDT/ this morning for INZ010-INZ011-INZ019. LM...None. && $$ Visit us at weather.gov/chicago