Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 28 2025 00:37:14 FOUS30 KWBC 280037 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 837 PM EDT Fri Jun 27 2025 Day 1 Valid 01Z Sat Jun 28 2025 - 12Z Sat Jun 28 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND NEAR SOUTHWEST VIRGINIA... ....Central & Southern Appalachians... A thunderstorm/heavy rainfall threat has become more focused as of late as very moist flow interacts with the terrain near a 'back-=20 door' cold front which is stalling across the region. Earlier=20 storms across West Virgina sent outflow boundaries down the front=20 to help with the consolidation in southwest Virginia. Efficient=20 hourly amounts up to 3" are possible in the very near term given=20 PWATs upwards of 2". Much of this region remains more sensitive to additional rainfall not only due to the typical terrain impacts=20 but a number of recent heavy rainfall events keeping FFGs low, with scattered to potentially numerous instances of flash flooding=20 possible. To the southwest, ongoing thunderstorms down the=20 foothills of the Appalachians into the AL Piedmont pose a Marginal Risk of excessive rainfall before CIN sets in later tonight. The Gulf coasts of AL & MS pose a similar risk during the early morning hours on Saturday due to onshore flow from the warm Gulf. Pulse-=20 type thunderstorms will have the ability to produce quick efficient bursts of heavy rainfall (1-3") and the risk for some mostly=20 isolated urban flooding, especially where any storms=20 develop/congeal along residual outflows. ....Northern Plains... A quick-moving shortwave across the northern tier of the country=20 is starting to lead to thunderstorm activity capable of locally=20 heavy rainfall, especially if convection can grow upscale into a=20 more organized MCS. However, prospects for flash flooding still=20 seem to be limited given the progressive nature of the shortwave=20 trough/possible MCS as noted in the 18z HREF probabilities of 0.5"+ of rain in an hour. A quick 1-3+" is likely anywhere over parts of the eastern Dakotas and across central Minnesota. ....In and near Oklahoma & Arkansas...=20 A couple rounds of convection -- one ongoing with an additional=20 flare up overnight in and near existing outflow boundaries near the Red River of the South and AR -- continue the need for a Marginal=20 Risk of excessive rainfall/flash flooding in and near portions of=20 eastern OK and AR through tonight. Hourly rain amounts to 2.5"=20 would be problematic in sensitive terrain and in urban areas. Roth Day 2 Valid 12Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHERN PLAINS AND UPPER MIDWEST, THE NORTHEAST, AND SOUTH- CENTRAL NEW MEXICO... ....Northern Plains and Upper Midwest... Next approaching upper shortwave trough, with a 90kt upper level jet streak on the lee side, will generate a compact area of fairly robust, transient deep-layer forcing over the outlook area into Saturday night. MUCAPEs are expected to soar within the warm sector prior to the surface cold frontal passage. Given precipitable water values getting near 1.75 inches...storms which form within the unstable airmass will be capable of producing rainfall rates in excess of 1 inch per hour and areal average rainfall amounts of 1 to 3 inches...especially once low- level inflow accelerates to between 30 kts and 40kts at 850 mb ahead of the approaching front with the potential for upscale/organized growth into one or more MCSs. The storm/mesoscale nature of the threat leads to uncertainty of a more focused corridor of higher risk, but a Slight Risk may be necessary particularly over the Upper Mississippi Valley if trends remain consistent in the guidance. ....Northeast... There continues to be an increasing concern for heavy to potentially excessive rainfall to develop across western Pennsylvania and surrounding areas as the frontal boundary sags southward and taps into the pooled PW values of 1.5-2". The latest model guidance are showing local maximums upwards of 2 inches possible and the ERO first guess supports expanding the Marginal Risk from eastern Pennsylvania further west into eastern Ohio, West Virginia and western Maryland. Further north, widespread convective activity across southeastern Canada north of the warm front looks to move into portions of northern New England. While guidance indicates the potential for 1-2" of rainfall totals across the region, the less robust convection on the northern side of the front should keep any flooding issues isolated. ....Southeast to the Mississippi Valley and adjacent southern Plains... Similar to day 1, scattered pulse thunderstorms are expected across a broad warm sector as seasonable instability develops with daytime heating from the Southeast west through the Mississippi Valley and into the adjacent southern Plains. High precipitable water values (~2", 2 standard deviations above the mean) will once again lead to highly efficient rain rates of 1-2" per hour, possibly as high as 3" per hour, which is more than enough to lead to isolated flash flooding concerns despite the generally limited thunderstorm duration. ....New Mexico... Yet another day of thunderstorms is expected across portions of southern New Mexico and west Texas with locally heavy rainfall (1-2") possible. QPF trends (coverage, intensity) are more isolated compared to day 1 with the moist south to southeast low-level upslope flow likely resulting in more localized areas of heavier rainfall focused across the Sacramento and Guadalupe Mtns south through the Trans-Pecos. The flash flood potential is expected to remain isolated. Putnam/Bann Day 3 Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING OVER PORTIONS OF THE CENTRAL UNITED STATES... There is a Marginal Risk of excessive rainfall over portions of the central United States from the western Great Lakes south through the Mississippi Valley and west into the central/southern Plains and southern Rockies. Showers and thunderstorms are expected both along and well-ahead of a cold front and trailing surface trough/dryline as an upper-level trough approaches from the west. Mechanisms to help focus convection becomes less defined ahead of the front but deterministic guidance indicates widely scattered rainfall totals of 1-3" are possible in an atmosphere characterized by precipitable water values in excess of 1.5 inches over all but the plains near the Central and Southern Rockies to in excess of 2 inches east of the Mississippi. Surface waves along the front may help to focus/organize convection and lead to a more concentrated threat. This is supported by localized maxima in the ensemble means/probabilities in the central Plains/Missouri Valley to the Upper Mississippi Valley region, but with low confidence in exact location at this point. Therefore, a broad Marginal Risk has been maintained for now. Putnam/Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9k_7878JXZq0tXxjek2i7rlPtiFabObuSV1nd2S8YBPu= Kj9YhvMVYaV92nTFscCz3WPfu-G74s1t9aHk62eWi1Mdo4w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9k_7878JXZq0tXxjek2i7rlPtiFabObuSV1nd2S8YBPu= Kj9YhvMVYaV92nTFscCz3WPfu-G74s1t9aHk62eWI3VO-28$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9k_7878JXZq0tXxjek2i7rlPtiFabObuSV1nd2S8YBPu= Kj9YhvMVYaV92nTFscCz3WPfu-G74s1t9aHk62eWQIeWfg0$=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .