Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 10 2025 07:39:53 FOUS30 KWBC 100738 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 338 AM EDT Thu Apr 10 2025 Day 1 Valid 12Z Thu Apr 10 2025 - 12Z Fri Apr 11 2025 ....OH Valley and Mid-South... The latest GOES-E WV suite shows a mid-level trough gradually=20 amplifying across the Midwest as shortwave energy digs=20 southeastward from the northern Plains. The model guidance shows a=20 further amplification of mid-level height falls down across the OH=20 Valley and Mid-South by later today and tonight which will allow=20 for a cold front and an attendant area of low pressure to cross=20 portions of the region. Locally heavy showers and thunderstorms are expected to develop in the warm sector this afternoon and evening=20 as a moderately buoyant airmass characterized by MLCAPE values of=20 1000 to 1500 J/kg sets up and couples with proximity of left-exit=20 region upper jet dynamics associated with the arrival of a jet=20 streak. Adding to the convective footprint will be steep mid-level lapse rates given the amplifying trough overhead, and a sufficient amount of shear will be in place for some supercell convection.=20 While moisture is not going to be particularly supportive of heavy=20 rainfall totals, the convection will be locally well-organized and=20 capable of producing some hourly rainfall totals of as much as 1 to 1.5 inches. Areas from KY/TN down through northern MS/AL will=20 generally see scattered pockets of this convection with this=20 rainfall potential. Given the wet antecedent conditions from the=20 most recent high-end rainfall/flooding event, it is possible that=20 these additional rains may result in an isolated concern for some=20 flash flooding. For now, a Marginal Risk will not be depicted given some question marks on the overall coverage of convection and=20 modest rainfall totals, but a non-zero threat of additional=20 flooding will exist at least on a small-scale and highly localized=20 basis. The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 2 Valid 12Z Fri Apr 11 2025 - 12Z Sat Apr 12 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-ATLANTIC STATES... ....Mid-Atlantic States... The 00Z model guidance continues to strongly support the arrival of an amplifying deep layer trough across the central Appalachians and the Mid-Atlantic states by Friday as an upper-level jet streak rounds the base of the trough and lifts northeastward up across the coastal plain. The model consensus suggests a 500mb low center developing=20 over the VA Piedmont area, however there is some latitudinal spread with this as some guidance like the 00Z NAM is farther south, and=20 other guidance like the 00Z GFS is farther north and faster.=20 Regardless of exact placement, large areas of the Mid-Atlantic=20 region will come under left-exit region jet dynamics for ascent=20 which coupled with strengthening frontogenetical forcing poleward=20 of a deepening area of low pressure, and relatively strong moisture convergence, should promote the development and expansion of=20 moderate to locally heavy rainfall. Instability will be lacking=20 over much of the region with exception of southern VA and=20 especially NC where closer proximity to the warm sector will be=20 noted. However, there will be steepening mid-level lapse rates=20 associated with the closed low development, and there will be areas of slow-moving, and rather shallow convection that will be capable of producing heavy rainfall rates. A few model solutions such as=20 the GEM regional, HRW-ARW2, and NAM-Conest support locally heavy=20 rainfall totals (2 to 4 inches) over parts of southwest VA and NC=20 in particular due to slow cell-motions. Farther north into the=20 cooler side of the storm, the I-95 urban corridor from central VA=20 up into southeast PA/NJ may see locally heavy rains impact this=20 region with totals as high as 1 to 2 inches. Generally, these rains should be beneficial aside from some localized urban runoff=20 concerns. However, there may be a more defined concern for some=20 localized flash flooding down into areas of southwest to south-=20 central VA and NC, along with some potential for southern WV to see some of this threat. Given the southward trends in the guidance=20 for the overall heavy rainfall footprint, the Marginal Risk area=20 has been accordingly shifted farther south compared to continuity. Orrison Day 3 Valid 12Z Sat Apr 12 2025 - 12Z Sun Apr 13 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_VPLyYCZtwqYV6fLA_IkBdrMDR4LJ_zURNtDbVo2JkLE= enzwLZ_9QO_N7kBhUUNxGuo6G_9VQpadSrKieL59TTYpj8Q$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_VPLyYCZtwqYV6fLA_IkBdrMDR4LJ_zURNtDbVo2JkLE= enzwLZ_9QO_N7kBhUUNxGuo6G_9VQpadSrKieL59-16sUnM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_VPLyYCZtwqYV6fLA_IkBdrMDR4LJ_zURNtDbVo2JkLE= enzwLZ_9QO_N7kBhUUNxGuo6G_9VQpadSrKieL59peFrngw$=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) .