Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 11 2025 00:47:28 FOUS30 KWBC 110047 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 847 PM EDT Sun Aug 10 2025 Day 1 Valid 01Z Mon Aug 11 2025 - 12Z Mon Aug 11 2025 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF KANSAS, MISSOURI, AND NORTHERN OKLAHOMA... 01z Update: Current radar and satellite composite indicate our setup across the Central Plains is continuing to evolve with the focus driven along a cold front analyzed over the southern tier of KS into southwest MO. Looking at mesoanalysis, there's a pretty strong corridor of sfc-850mb FGEN situated over southeastern KS into neighboring MO with blossoming convection over the above areas with radar estimates of 2-3"/hr in the strongest cores. Elevated PWATs and considerable theta_E presence along and south of the front lend credence to a fairly robust convective environment capable of dropping significant rainfall in a span of a few hrs. The signal for heavy rain back over southwest KS remains with upscale growth anticipated out of the southeast CO Front Range, migrating eastward along the confines of the boundary. This eventual complex will merge downstream with the convective pattern ongoing across the other side of KS, congealing into quite a large convective cluster as we move beyond 06z. Cold pool generation will span eastward with some inference of a MCV potentially materializing out of the leftover convective pattern, but that jury is still out. Regardless of the eventual evolution, there's a consensus on a large area of 2-4" with locally upwards of 6-7" across the south-central and southeast KS into the far southwestern portion of MO by the end of the forecast cycle.=20 Pending outflow progression to the north, new cells could=20 materialize within the upstream cold pool progression, likely=20 accenting the frontal boundary to waver further north towards the=20 I-70 corridor. This could be in part to the mesoscale low generated off the convective cluster anticipated later which could enhance a secondary convective cluster on the arcing frontal positioning as=20 the boundary gets lifted north-northwest. This puts places like=20 Kansas City to Topeka in play for heavy thunderstorm potential=20 later this evening, in agreement with the latest AIFS ML output=20 signaling a better 6hr QPF output across northeast KS for the=20 period between 06-12z and beyond. Considering the overall evolution anticipated and observational trends, there was not a need to deviate much from the previous MDT risk forecast with only some minor adjustments on the edges to account for the latest trends.=20 SLGT risk is very much in place for much of KS into portions of OK=20 into MO for the rest of the overnight with a high-end SLGT risk=20 (25-40% threshold) for flash flood potential as far north as I-70=20 over central and northeast KS into MO.=20 SLGT risk remains in effect across the Midwest as thunderstorm activity continues to plague areas of IA into WI and IL. This is trending to be the last round before conditions settle, but with the antecedent moist soils remaining from the previous 36-48 hrs of rainfall, there was little reason to remove the previous SLGT risk in place until the setup finally vacates. Thus, maintained general continuity and scaled back over areas where convective impacts are less likely.=20 SLGT across the Southeast CONUS remains with the greatest threat remaining along the immediate coastal plain from Wilmington, NC down through Brunswick, GA. Some of the hi-res guidance continue=20 to promote these smaller heavy cores to brush into the coast during the overnight hrs. which could very well amount to significant=20 rainfall in a short time considering the environment maintaining PWATs running >2.25" as noted via the 00z soundings from KJAX and KCHS. It's a case where onshore flow will have the ultimate say in what occurs in this setup as thunderstorms could stay offshore all night, but the proximity of the heavy convection and potential are too close to deviate away from what was inherited. Continuity was maintained as a result with agreement from the local WFO's. MRGL risk remains across the Southwest CONUS into the Caprock of NM/TX where isolated heavy cores could offer some low-end opportunity for flash flooding. This setup will dwindle after 06z with the loss of diurnal instability and surface inversion development.=20 Kleebauer Day 2 Valid 12Z Mon Aug 11 2025 - 12Z Tue Aug 12 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS THROUGH THE UPPER MIDWEST, THE COASTS OF THE CAROLINAS, & THE FLORIDA PANHANDLE... ....Southern Plains & MO-KS-AR-OK... The South Central U.S. will be sandwiched between two upper level disturbances; one upper trough approaching from the Southern Rockies, and mid-upper level trough axis over southern Texas. Atop the atmosphere, modest diffluent 250mb flow will support divergence aloft while a nearby surface frontal boundary acts as a trigger for thunderstorms. Any residual outflow boundaries from Sunday night's convection or from Monday afternoon's convection will also likely play a role in firing off thunderstorms to the south and east of the surface front. PWATs will generally be >1.8" along the Red River and points north and east, while areas as far west as the TX Panhandle and cap rock are between 1.4-1.6". In terms of instability, lesser values (MLCAPE 500-1,000 J/kg) will be available in the TX Panhandle, with greater over the MO-KS-AR-OK region through Monday night. The 12Z HREF does show spotty areas of moderate-chance probabilities (40-60%) within the Slight Risk area for >3" of rainfall, as well as low-chance probabilities (10-30%) for >5" in central OK. Given these factors, the Slight Risk was focused more here compared to the previous forecast cycle. ....Middle MS Valley... The Slight Risk was scaled back here given the reduction in available instability, latest QPF reduction, and lesser footprint of >3" rainfall probabilities in the 12Z HREF. With soils growing more saturated and the lingering presence of near 2" PWATs, there is still a localized flash flood threat, hence the presence of a rather large Marginal Risk area that stretches from the I-70 corridor from KS/MO on north through the Great Lakes. ....Florida Panhandle & Big Bend... In coordination with TAE, introduced a Slight Risk for areas along and south of I-10 in the FL Panhandle and Big Bend. As a mid-to- upper level inverted trough axis approaches, it will be accompanied by a wealth of anomalous PWATs that will approach 2.5" in some areas. Modeled soundings show warm cloud layers just shy of 16,000ft deep in some cases with little-to-no capping inversions Monday afternoon. On the eastern flank of the inverted trough, 925-850mb winds will be uniformly out of the SE. ECMWF soundings over the Big Bend show Corfidi Upshear vectors that are <10 knots Monday afternoon, suggesting the potential for back-building and training thunderstorms. Given the abundance of tropical moisture and MLCAPE up to 1,000 J/kg, it is quite possible to have thunderstorms generate 2" of rainfall in as little as 30 minutes. The scale of these storms are making QPF forecasts across CAMs guidance widely varying on location, but the atmospheric parameters support an increasingly concerning setup for flash flooding for Monday. Mullinax ---Previous Discussion--- ....Southeast... Yet another active day across the Southeast is expected Monday as an inverted low-to-mid level trough drifts northeast along the coast of the Carolinas. This trough will move within a favorable thermodynamic environment characterized by still highly anomalous PWs of 2 to 2.25 inches, although the slow retreat of the mid-level ridge to the east should help ease some of this moisture the latter half of D2. Still, the overlap of these elevated PWs with MUCAPE of 1000-2000 J/kg will support convection with heavy rainfall. In general, convection across the Southeast on Monday should be scattered in coverage, but some organization, or at least better clustering, is likely in the vicinity of any shortwaves and the inverted trough, primarily from the Grand Strand of SC to the Crystal Coast of NC. Here, repeating rounds of convection with efficient rain rates exceeding 2"/hr are likely, driven by impressive low-level confluence. Elsewhere across the Southeast, heavy rainfall rates are also likely, but with less organization, but still slow storm motions. The rainfall probabilities for more than 3" peak along the SC/NC coasts and the SLGT risk was adjusted cosmetically for the new guidance. Otherwise, a broad MRGL risk continues for slow moving thunderstorms across areas that have had recent heavy rainfall, and an expansion was made into the Upstate of SC where some of the high res CAMs suggest enough upslope to enhance rainfall locally in that area. Weiss Day 3 Valid 12Z Tue Aug 12 2025 - 12Z Wed Aug 13 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE UPPER MIDWEST/GREAT LAKES, THE SOUTHWEST, AND GULF COAST/SOUTHEAST... 2030Z Update... There were some minor adjustments made this forecast cycle to the Marginal Risk areas based on latest 12Z guidance and WPC QPF. The Southeast will be closely monitored given the same feature supporting a Slight Risk on Day 2 in the FL Panhandle and Big Bend areas will move farther inland on Tuesday. However, there remains a fair amount of spread regarding how much rainfall occurs and which areas are favored. Given the lingering uncertainty, opted to hold on to a Marginal Risk area with no upgrade this forecast cycle. Mullinax ---Previous Discussion--- ....Upper Midwest... The anomalous mid-level trough that will produce the heavy rainfall D1 and D2 across the Upper Midwest/Central Plains will weaken Tuesday as shortwaves embedded within the trough become more rapidly absorbed into westerlies across the northern tier of the CONUS. A lingering shortwave trough, likely convectively enhanced, pivoting across KS/MO will drive sufficient ascent for additional rainfall along the weakening front, but with lesser moisture and instability than was available earlier in the week. Still, at least short term training of intense rainfall rates is likely as mean layer winds align to the weakening front, which could result in isolated instances of flash flooding. ....Southeast... Elongated mid-level ridge extending westward from the Atlantic to along much of the Gulf Coast will subtly retreat Tuesday as a shortwave emerging from the Gulf lifts northward. The modest height falls and PVA accompanying this feature will drive ascent into an otherwise weakly forced environment, producing a favorable setup for scattered to numerous thunderstorms from the central Gulf Coast northeast along the periphery of the ridge into Georgia. Thunderstorms that develop will contain heavy rainfall rates of 1-2"/hr in response to favorable thermodynamics characterized by PWs of 2-2.25 inches overlapping MUCAPE as high as 2000 J/kg. The general SW return flow will push storms along steadily to the N/NE, but with repeating rounds possible and some organization beneath the shortwave, a few instances of flash flooding could result as rainfall reaches 2-3" in some areas. ....Southwest... Mid-level ridging will expand but shift subtly westward on Tuesday while weak impulses rotate around its periphery. This will help to intensify instability across the region, and progs indicate a larger plume of 1000 J/kg MUCAPE spreading across the southern portions of AZ and NM, especially during peak aftn heating. This will combine with PWs that will be above 1" in many areas south of the Mogollon Rim, leading to a favorable environment for convection. Where any of these impulses rotate aloft, enhanced ascent will yield scattered to widespread thunderstorms with rain rates approaching 1"/hr at times, and these storms will move slowly/chaotically beneath the ridge. This could result in isolated instances of flash flooding, most likely where any storms track across more vulnerable terrain features or burn scars. Weiss Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!50RC5MywqURfpOOL3cZQ-ASMtdIqGbPFlyHbXUAa38Fu= Jz9PNkHCncayFOtPRF-QjKmJiYqZwWFQEy1E1zFSkAV1AJc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!50RC5MywqURfpOOL3cZQ-ASMtdIqGbPFlyHbXUAa38Fu= Jz9PNkHCncayFOtPRF-QjKmJiYqZwWFQEy1E1zFSFoctSXk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!50RC5MywqURfpOOL3cZQ-ASMtdIqGbPFlyHbXUAa38Fu= Jz9PNkHCncayFOtPRF-QjKmJiYqZwWFQEy1E1zFS4pWYRxg$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .