Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 23 2025 00:52:32 FOUS30 KWBC 230050 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 850 PM EDT Tue Apr 22 2025 Day 1 Valid 01Z Wed Apr 23 2025 - 12Z Wed Apr 23 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTH... ....01Z Excessive Rainfall Discussion... Returned to having two Marginal Risk areas with the loss of daytime heating/instability...namely along/near the Gulf coast and Lower Mississippi Valley as well as across parts of West Texas into the Southern Plains. The convection that persists into the late evening/early morning hours from Louisiana and southeast Texas should continue to focus along and south of a quasi-stationary boundary stretching from the Lower Mississippi Valley into the southern Appalachians. From parts of West Texas eastward into=20 Oklahoma and should be developing along and east of a progressive=20 dry-line and then expanding eastward as the low level jet develops=20 later tonight. As mentioned previously...the some of the areas=20 where convection develops later tonight have notably lower flash=20 flood guidance but the signal for heavy rainfall amounts/rates is=20 less not as stong. Bann Day 2 Valid 12Z Wed Apr 23 2025 - 12Z Thu Apr 24 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE PLAINS AND THE SOUTHEAST... ....19Z Update... The inherited Marginal Risk was greatly expanded towards the south and east with this update. The area now includes much of northern and eastern Texas, and the northern portions of the Southeast through into the Carolinas. This eastward expansion has largely to do with the increasing Gulf moisture streaming north into the Southeast with a very persistent souther LLJ, and a similarly persistent stationary front that will remain draped across the Southeast. The clash of this warm and humid air with the front will cause a renewed round of showers and thunderstorms from east Texas through to the Carolinas. While the large-scale pattern favors more slow-moving training thunderstorms, there is significant disagreement in the guidance as to what form those storms will take, whether groups of cells and MCSs interact, and ultimately where these interactions may occur. Since the front remains in place, the storms are likely to move over many of the same areas being impacted by ongoing showers and storms this afternoon, which locally increases the flash flooding risk. There is somewhat better agreement in the guidance that the wettest areas will likely focusing into southern Nebraska and northern Kansas on Wednesday. This too will be the result of an MCS or clusters of thunderstorms developing and training multiple times over the same areas. The Marginal remains in place as the consensus of heaviest rains on the order of 1-2 inches (locally higher, of course) is in a portion of Kansas and Nebraska that has largely missed out on recent heavy rainfall, and the antecedent dry conditions should help to offset and delay the greatest impacts from any heavy rain. The area of the Marginal of least concern appears to be over Oklahoma, which while seeing some scattered shower and thunderstorm activity, should be between the MCSs/areas of more organized and persistent convection. However, due to heavy rainfall, lower FFGs over much of the state lower the threshold needed to achieve flash flooding, so the Marginal is largely unchanged there. Wegman ....Previous Discussion... Several shortwaves will be exiting the Rockies throughout the day with several pockets of convective development sprawled across the Central and Southern High Plains by the evening hours. While the confidence continues to be lower on the maximum amounts there is however higher confidence on the potential for scattered flash flood prospects. Although the location of QPF maxima vary, there is a general consensus of a widespread 1 to 2 inches from the Front Range of Colorado/Wyoming/Nebraska south to the Red River Basin near Texas to Kansas/Oklahoma. Some of these areas will have seen significant rainfall prior to any additional impacts leading to some localized lower FFG indices once the event occurs. The inherited Marginal continued to mostly highlight areas across the Plains that had an elevated threat for heavy rainfall and flash flooding. The latest guidance and WPC QPF trended higher with QPF over northeast Kansas, southern Nebraska, southwest Iowa and northwest Missouri. As such, the Marginal Risk area was modified to encompass that part of the region. Campbell/Kleebauer Day 3 Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF KANSAS, OKLAHOMA, ARKANSAS AND MISSOURI... ....19Z Update... Multiple clusters of thunderstorms will likely be ongoing in different portions of the ERO risk areas at the start of the Day 3/Thursday time period. These MCS's will likely weaken and dissipate through the late morning, as MCS's typically do. However, with peak heating and the increased instability associated therewith, renewed rounds of showers and thunderstorms will redevelop. Since this is likely to occur over many of the same areas hit with heavy rain both now and on D2/Wednesday, this will once again renew the potential for localized flash flooding over portions of the Southeast. For the Slight Risk area, these showers and storms will likely redevelop in areas particularly forecast to be hard hit with heavy rain from the D2/Wednesday time period, along with the potential for a new MCS to form Thursday night, resulting in more widespread heavy rainfall. Thus, the Slight Risk was maintained where it was already issued, and expanded south and east with this update into more of Missouri, Arkansas, and Oklahoma. This expansion is largely a function of much of this area being hit with heavy rain a few days ago, and the rivers will not have fully drained, and the typical evolution of MCSs in the guidance to trend south with time. For all areas, the LLJ out of the Gulf will tap into some of the deepest moisture yet as compared with the previous two days. This will support both heavier rainfall with the strongest storms, and greater coverage of showers and storms in general. Due to inherent uncertainties with how the MCSs/storms will evolve and interact with each other, at this point it appears unlikely additional upgrades to a Moderate will be needed, as errors in thunderstorm placement and coverage are high by the Day 3 period. However, should the forecast remain wet and rainfall from the current D1 and D2 periods outperform, then a targeted Moderate Risk cannot be completely ruled out by the time more of the CAMs have a chance to analyze the weather pattern. Wegman ....Previous Discussion... The pattern will be favorable for multiple rounds of showers and thunderstorms to move through the south-central U.S. With a moist, unstable flow expected and shortwave energy passing through heavy rainfall will likely develop across the region which may lead to local flash flooding. Areal averages of 1 to 2 inches are forecast with locally higher amounts possible. A Slight Risk for excessive rainfall is in effect for a large portion of Kansas, northern Oklahoma, far northwest Arkansas and western Missouri. A Marginal Risk area spans from northern Texas to southern Nebraska and extreme southwest Iowa. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_Cz4O4QnkZQhrrzG8eEOVWKZvuirFIGiiFbNF-vgT1wy= mnu4VrAKbsbpugHjCnEfFmiLh_kx4S7bpUfihdalLUAP8Ow$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_Cz4O4QnkZQhrrzG8eEOVWKZvuirFIGiiFbNF-vgT1wy= mnu4VrAKbsbpugHjCnEfFmiLh_kx4S7bpUfihdalBYFTEus$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_Cz4O4QnkZQhrrzG8eEOVWKZvuirFIGiiFbNF-vgT1wy= mnu4VrAKbsbpugHjCnEfFmiLh_kx4S7bpUfihdalek9bs8w$=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) .