Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed May 28 2025 21:45:32 FOUS30 KWBC 282144 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 544 PM EDT Wed May 28 2025 Day 1 Valid 2133Z Thu May 29 2025 - 12Z Thu May 29 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF CENTRAL TEXAS AS WELL AS SOUTHWESTERN KANSAS... The Slight risk was maintained over portions of central TX, although do generally consider this a lower end Slight risk. Isolated to scattered convection the next few hours will result in some flash flood risk with cell mergers probable. However this=20 convection is fighting mid level dry air and some subsidence behind the Gulf Coast MCV...thus unclear how organized this convection=20 will get. It seems most likely that activity will not be as=20 organized as the past couple nights, with limited upscale growth=20 keeping the flash flood risk on the lower end of the Slight risk=20 scale...however we will continue to monitor convective trends. The Slight risk over KS was maintained, but shifted a bit=20 southwest to better align with the axis of grater instability.=20 While some upscale growth into a MCS or convective cluster is=20 likely, this activity should stay quick moving limiting the=20 magnitude of any flash flood risk. Thus primarily looking at high=20 rainfall rate driven minor flooding of urban and/or low lying=20 areas as the main threat tonight. However, through the evening as=20 convection increases in coverage and organizes, we could see cell=20 mergers result in an isolated/scattered flash flood risk over=20 western KS and possibly far eastern CO. Isolated flash flooding will remain possible over portions of LA=20 and MS as well...although generally quick northward propagation of convection should limit this threat. Chenard Day 2 Valid 12Z Thu May 29 2025 - 12Z Fri May 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE SOUTHEAST... ....19Z Update... The inherited Slight Risk area was removed with this update. The latest CAMs guidance for the period shows that the shortwave driving expected convection through the period will weaken, and struggle to organize the convection ahead of the surface cold front in such a way as to promote a greater than isolated flash flooding threat. FFGs across much of the Southeast, while slightly depressed from earlier rainfall, have largely recovered and while soils are a bit wetter than normal, the lack of organization should hold any flash flooding to isolated instances. Thus, the combination of high FFGs and no consistent signal of heavy rainfall should preclude more widespread Slight Risk impacts. For the Gulf Coast, the urban centers in the area will have the greatest threat for flash flooding, but that assumes the storms linger over those urban areas long enough to cause flash flooding. Conversely, the surrounding Marginal Risk was expanded to include more of the harder hit areas of Texas and the portions of the Mid- Atlantic that got a good soaking rain this morning. The disorganized nature of the afternoon convection could cause isolated flash flooding in these areas should the storms form over particularly sensitive areas. A secondary area of convection that begins its life in Kansas tonight will move across Missouri and eventually move into Kentucky and Indiana Thursday night. This more organized convection will locally increase the flash flooding threat compared to many other parts of the Marginal Risk area. However, these storms will be quite progressive, so defining where a potential Slight Risk with these storms is also not possible at this time, but the area will be monitored. Instability on the northern side of the complex will likely further hamper the storms' ability to produce rainfall amounts needed to cause flash flooding. Throughout the Marginal Risk area, it's probable, if not likely that locally storms will organize enough to cause Slight Risk impacts, but where that will occur is highly uncertain at this time. Wegman Day 3 Valid 12Z Fri May 30 2025 - 12Z Sat May 31 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID ATLANTIC, OHIO VALLEY, AND SOUTHEAST... ....19Z Update... No major changes were made to the inherited Marginal Risk area along the Mid-Atlantic and Southeast. The Marginal was expanded a bit due to convective uncertainty across the Southeast, while in the Mid-Atlantic the complex of storms from the Ohio Valley will continue across the area through the period. Once again, the storms should be moving fast enough to preclude anything other than isolated flash flooding, with the urban centers at a bit higher risk for flooding. Wegman ....Previous Discussion... A potent mid-latitude trough will pivot through the Ohio Valley on Friday morning with a broad axis of diffluence downstream of the mean trough leading to a large scale forcing regime that will enhance regional precip field across the Mid Atlantic. At the surface, low pressure will navigate into the Mid Atlantic with a trailing cold front migrating eastward through much of the Eastern CONUS, interacting with a wedge of low to mid-level instability situated over the Central/Southern Appalachians and points east. Greatest thermodynamic alignment will likely be closer to the coastal plain, but elevated MUCAPE signatures can be found within the Mid Atlantic Piedmont and under the primary trough. The tandem of increased sfc-500mb forcing from the trough/front combo will lead to a scattered to widespread convective pattern that will induce locally heavy rainfall and potential for flash flooding. Timing of the ascent pattern and frontal progression will be key in determining the logistics of where the main axis of convection will occur. As of now, the best chances for convectively driven heavy rain are within the Central and Southern Appalachians, Southern VA through the NC Piedmont, and the Eastern Carolinas up to the VA Tidewater. These are the areas conducive for flash flooding at this time with localized amounts reaching 2-3" in the places hit the hardest. 1-2" is more likely out in the terrain of the Apps, but that is a signal sufficient for flashier responses due to the complexity of the topography. Despite the questions of timing, the threat remains leading to a broad MRGL risk over much of the Mid Atlantic with a southern inflection down towards FL as the trailing front will move through the region and interact with a deeper moisture layer and plentiful instability to induce some heavier convective cores capable of flash flooding in more urbanized zones. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6uesgqpClYcSkJkcTBsE7SDnZEoTshrzS75su3qR32YJ= xnmA6hD_1_TfkHULkTtregkq-qjjbKThRxgKOQxCrZsCsJg$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6uesgqpClYcSkJkcTBsE7SDnZEoTshrzS75su3qR32YJ= xnmA6hD_1_TfkHULkTtregkq-qjjbKThRxgKOQxCs_qZLO4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6uesgqpClYcSkJkcTBsE7SDnZEoTshrzS75su3qR32YJ= xnmA6hD_1_TfkHULkTtregkq-qjjbKThRxgKOQxC2yQNfhw$=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) .