044 FXUS63 KLOT 102317 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 617 PM CDT Sun Aug 10 2025 .KEY MESSAGES... - Periodic bouts of scattered showers and isolated to scattered thunderstorms can be expected through the first half of the upcoming work week, probably followed by a few quieter days. - Any stronger thunderstorms the next few days will be capable of producing torrential downpours and localized flooding. && .DISCUSSION... Issued at 301 PM CDT Sun Aug 10 2025 Through Monday: In the wake of the earlier showers and storms, convective coverage has greatly diminished as of this writing, owing to likely subsidence amidst marginal mid-level lapse rates. Isolated to widely scattered showers and perhaps a few isolated thunderstorms should be the theme for the rest of the afternoon hours. Can`t completely rule out an isolated thunderstorm as far southeast as the Kankakee River Valley of northwest Indiana over the next few hours. Looking off to the west of the MS River, a slow moving MCV over eastern Iowa has recently resulted in the initiation of scattered convection. Given the worked over and more stable conditions over much of northern Illinois, along with this wave approaching after dark, how much bonafide deep convection is able to develop in our CWA is a big question mark. The next shift will be able to better refine things per observational trends this evening. Given the uncertainty, weak lapse rates, unfavorable timing, and only modest forcing, kept thunder chances in the slight chance range through tonight and into Monday morning. Our highest forecast PoPs (30-50%) for shower activity regardless of thunder chances/coverage are once again focused near/northwest of I-55. The slow moving cold front up across the upper MS Valley will gradually progress southeast through Monday. Specifics regarding shower and thunderstorm trends in the afternoon are unclear. However, outflow could push the effective boundary farther south resulting in better chances for scattered showers and thunderstorms farther south than previous forecast thinking. Exactly how things play out overnight into the morning hours will help determine how the rest of the day goes. All in all, weak forcing, possible cloud cover effects, and increased uncertainty necessitated lowering PoPs down into the 30-40% range through the day on Monday. If and where thunderstorms develop, coverage now appears more likely to be widely scattered in nature. Marginal mid-level lapse rates and sub marginal deep layer shear should further limit the threat for any damaging downburst winds on Monday. Slow storm motions and high PWATs will keep the threat for localized torrential downpours and flooding going, however. Aside from the uncertain convective details on Monday, it will be another warm and humid day, especially near and southeast of I-55 (upper 80s to around 90F). Castro Monday Night through Sunday: The potential for continued off-and-on rounds of showers and thunderstorms will persist through Tuesday night/Wednesday as an axis of high theta-e air with PWATs near 2 inches remains nearly quasistationary overhead. Several perturbations will slingshot their way through fairly active southwest flow during this time frame, as a robust shortwave drops out of southern Canada and sweep through the northern Plains. Timing each of these individual perturbations remains challenging, as, to some degree, convective augmentation will take place each day with successive rounds of thunderstorm development. That said, there is a decent signal in latest model guidance that a synoptic wave (positively tilted in most guidance) may impinge on the region Monday evening and overnight, yielding an uptick in broad warm and moist advection and an associated increase in shower and some thunderstorm activity. The ensemble signal remains fairly strong that the greatest potential coverage during this period overnight Monday night into Tuesday morning will remain near and northwest of I-55, within the core of the modeled deepest tropospheric moisture. While 925-850 mb southwesterly flow will be seasonably strong (near 35 kts at times), not currently seeing signs of particularly robust convergence axes which would spell more of a concerning heavy rain and flood scenario. Some training of individual convective clusters will be possible with cloud-bearing flow generally southwest to northeast, aligned parallel with the main moist axis, but nothing currently stands out as overly concerning from a widespread flash flood perspective into Tuesday. Guidance remains in decent agreement that a cold front will press south through the region during the Tuesday night/Wednesday timeframe. This should shift the shower and thunderstorm chances southward Tuesday afternoon and eventually bring an end to the daily convective potential. If the front gets hung up in our far south on Wednesday, isolated afternoon showers and thunderstorms will be possible. Moisture and instability looks like it`ll end up sloshing back across the region towards next weekend. Current extended guidance suggests that our region may remain on the northern periphery of lingering subsidence with a belt of stronger cyclonic mid and upper level flow displaced across northern Wisconsin and the UP of Michigan. This may end up keeping the more appreciable storm chances to our north, although there are some signals that the mid-level ridge could break down towards the Saturday night - Monday time frame ahead of another front which could open us up to the next round of MCS chances. Carlaw/Castro && .AVIATION /00Z TAFS THROUGH 06Z TUESDAY/... Issued at 617 PM CDT Sun Aug 10 2025 A warm and moist airmass remains stalled over the region ahead of a stationary front draped across the Upper Mississippi River Valley. Small-scale perturbations and axes of confluence will afford periodic opportunities for showers and thunderstorms amidst otherwise prevailing dry conditions. One such confluence axis has recently allowed for isolated showers and storms to develop from IJX to ARR. This activity should lift east- northeastward and threaten DPA/ORD and possibly MDW between 00 and 02Z. Meanwhile, an MCV in eastern Iowa is supporting the development of a broken band of showers and storms near the Mississippi River, which will threaten RFD between 02 and 04Z. For both of these areas, will introduce TEMPO groups at DPA/ORD/RFD. Thereafter, will revert to a strategy of prevailing dry conditions until new mechanisms to initiate convection become apparent or trends dictate otherwise. Winds through the TAF period are expected to remain out of the southwest. Periods of mid to upper level clouds will prevail. High resolution guidance suggests a period of IFR cigs may develop in the vicinity of RFD overnight in response to weak winds, moist soils, and low pressure troughing in southern Wisconsin. At this point, confidence is not high enough to introduce a formal mention of such in the outgoing TAF package. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago