Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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840 FXUS63 KLOT 140538 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1238 AM CDT Wed Aug 14 2024 .KEY MESSAGES... - Showers and storms likely late Wed night into Thursday AM, locally heavy rainfall possible. - Second round of showers and storms likely late Thursday, mainly during the evening and night, some could be strong to severe with locally heavy rainfall. - Widely scattered showers and a few storms Friday-Sunday afternoons/evenings. && .DISCUSSION... Issued at 320 PM CDT Tue Aug 13 2024 Through Wednesday: No impactful weather is expected through the daytime tomorrow as surface high pressure continues to slowly drift eastward through the region. Still can`t rule out some stray showers popping along the lake breeze or any other subtle convergence zones farther inland this afternoon as has been seen in southeastern Wisconsin, but otherwise, favor a dry forecast through tomorrow afternoon. High temperatures tomorrow should be just a touch warmer than they were today at most locations, with cirrus debris from convection to our southwest likely to blunt solar insolation just enough to prevent temperature readings from making a run at 90 degrees. Ogorek Wednesday Night through Tuesday: Focus in the extended forecast period remains the potential for a couple rounds of showers and thunderstorms late Wednesday night through Thursday night. At the beginning of the period a mid-upper shortwave ridge and surface high pressure will be in the process of shifting east of the region in response to an approaching upper level trough/developing low. An associated surface low is forecast to lift northeast through Minnesota with a lead warm front lifting across the region bringing a return to warm and humid conditions (low 70s dewpoints) to the local area and set the stage for possible strong to severe thunderstorm development and heavy rainfall. There continues to be an array of potential outcomes for the first round of storms as an upstream MCS tracks into the area. This includes anything from the MCS decaying as it moves into the area (particularly on the northern extent) to a more persistent cluster of showers and thunderstorms moving across the entire forecast area. There remains a signal for a lull in activity during the afternoon hours before a likely second round of showers/storms during the evening hours. The strength of these storms and overall coverage ultimately depends upon what transpires in the morning hours. A slower exit and greater coverage could limit our destabilization and reduce the evening storm severity and coverage. Meanwhile, less coverage and quicker ending AM storms could allow for stronger destabilization aided by steeper lapse rate plume advecting into the area. This would support the higher-end instability values depicted by some model guidance. This unstable airmass coincident with increasing deep layer shear with the approaching wave as well as some low-level shear (increasing LLJ), would supportive of all severe hazards. Overall, will begin to message the potential for strong to severe thunderstorms, though this threat remains conditional. Looking more specifically at the heavy rain potential, a higher-end thunderstorm training event does not appear to be the most likely outcome (based on the latest guidance) when comparing this set-up to our typical Maddox patterns for flash flooding. Modeled PWATs will be toward the upper echelon for this time of year, however, and suggests any storms that develop will be capable of high rainfall rates and any training of storms in this environment would support at least a localized flash flooding threat. Friday through the weekend the closed mid-upper low will meander across the Great Lakes region which likely will allow for diurnal scattered showers and isolated thunderstorms each day. Beyond Friday temperatures will be in the 70s to low 80s through the end of the period. Petr && .AVIATION /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 1237 AM CDT Wed Aug 14 2024 VFR conditions are expected through tonight, though patchy MIFG cannot be ruled out at RFD toward daybreak. VRB winds under 5 knots (favoring the SE quadrant) will persist through this morning as a surface ridge continues to drift northeast of the area. Expect a lake breeze with E winds 10 to 15 knots to cross ORD/MDW early this afternoon before settling back to SE under 10 knots this evening. Near or just after the end of the forecast period (12Z Thursday), a line of decaying SHRA with SE gusts around 20 knots should affect the terminals. TS was not included in this forecast with the potential expected to be less than 20%. Kluber && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at weather.gov/chicago