Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Apr 11 2025 00:40:00 FOUS30 KWBC 110039 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 839 PM EDT Thu Apr 10 2025 Day 1 Valid 01Z Fri Apr 11 2025 - 12Z Fri Apr 11 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley 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... ....2030Z Update... Previous forecast remains on track overall, including continued support from the hi-res guidance for a more southerly QPF footprint from the central/southern Appalachians east-northeast through North Carolina and into the southern Mid-Atlantic, which led to minimal spatial changes to the inherited Marginal Risk. A combination of showers and some thunderstorms will support areal average rainfall totals of 1-2", with amounts locally as high as 3". However, generally expect rain rates to remain moderate and on the steady side, especially on the western/colder side of the system, with isolated heavier rain rates of around 1" per hour likely limited to areas along and east of I-95 where some instability will be present. As noted in the prior discussion, this steady rainfall will likely be more beneficial for most areas, but some isolated urban flooding/ponding will be possible particularly along the I-95 corridor, and possibly for more terrain sensitive areas into the Appalachians of southwestern Virginia and southern West Virginia. Putnam ....Prior Discussion... ....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 over the VA Piedmont area, however there is some latitudinal spread with this as some guidance like the 00Z NAM is farther south, and other guidance like the 00Z GFS is farther north and faster. Regardless of exact placement, large areas of the Mid-Atlantic region will come under left-exit region jet dynamics for ascent which coupled with strengthening frontogenetical forcing poleward of a deepening area of low pressure, and relatively strong moisture convergence, should promote the development and expansion of moderate to locally heavy rainfall. Instability will be lacking over much of the region with exception of southern VA and especially NC where closer proximity to the warm sector will be noted. However, there will be steepening mid-level lapse rates 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 the GEM regional, HRW-ARW2, and NAM-Conest support locally heavy rainfall totals (2 to 4 inches) over parts of southwest VA and NC in particular due to slow cell-motions. Farther north into the cooler side of the storm, the I-95 urban corridor from central VA up into southeast PA/NJ may see locally heavy rains impact this region with totals as high as 1 to 2 inches. Generally, these rains should be beneficial aside from some localized urban runoff concerns. However, there may be a more defined concern for some localized flash flooding down into areas of southwest to south- central VA and NC, along with some potential for southern WV to see some of this threat. Given the southward trends in the guidance for the overall heavy rainfall footprint, the Marginal Risk area 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. Putnam Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_FSg4uTJFFnrYwANTLW5Msc8XxIdXs3wClTvOKZ_nsT2= cjmGAH4lrqyu9d9fbjpS7DeAphc6YeEmAjhNemLtZFe0IPs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_FSg4uTJFFnrYwANTLW5Msc8XxIdXs3wClTvOKZ_nsT2= cjmGAH4lrqyu9d9fbjpS7DeAphc6YeEmAjhNemLtkEX4yFA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_FSg4uTJFFnrYwANTLW5Msc8XxIdXs3wClTvOKZ_nsT2= cjmGAH4lrqyu9d9fbjpS7DeAphc6YeEmAjhNemLtdVhLGfc$=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) .