Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Apr 11 2025 15:30:14 FOUS30 KWBC 111530 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1130 AM EDT Fri Apr 11 2025 Day 1 Valid 16Z Fri Apr 11 2025 - 12Z Sat Apr 12 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC... 16Z Update: Our current upper level and surface progression across the Ohio Valley and Mid Atlantic will maintain an evolution capable of prolonged moderate to heavy rainfall across eastern half of VA up through the DMV and Delmarva areas the next 12-18 hrs. This evolution will eventually pivot further north into the Northern=20 Mid Atlantic and Northeastern U.S. as we move into the late- afternoon and evening time frame as the mid and upper level pattern continue to mature with a slowly amplifying surface progression maneuvering off the eastern seaboard. An axis of heavier rainfall continues to migrate northward within the meridional regime on the=20 eastern flank of the shortwave trough centered over the Ohio=20 Valley. This will continue for several more hours prior to a more textbook deformation precip orientation with a pivoting precip field with embedded stronger banding structures that will align south-southwest to north-northeast within the western flank of the low. This will lead to extended heavy rain prospects across NoVA up through Central MD into the Delmarva with a corridor of heavier rates likely over Southeast PA by nightfall.=20 As currently forecast, we've come into good agreement within the 12z deterministic suite on the magnitude of the rainfall with totals of 1-2" (Locally higher) situated within that corridor above. Considering the current evolution, radar presentation, and general expectations of totals/rates, the MRGL risk inherited was relatively maintained with the removal of the NC area due to precip moving out of those zones leading to no anticipated impacts the=20 rest of the period.=20 Kleebauer=20 ...Previous Discussion.. A slow-moving, amplifying upper level trough parked over the eastern half of the country will direct a southerly jet streak along the coast. This jet streak will work to cause the trough to become more negatively tilted with time, though it will really be neutrally tilted. Regardless, the jet streak combined with the cold air in the trough and a developing upper-low-esque circulation in the upper levels will support the development of a slow moving coastal low along the Carolinas this morning. As divergence increases and the low continues to pick up Gulf Stream moisture, the precipitation shield will expand over much of the Delmarva west to the I-95 corridor. For most areas, this will mean a prolonged period of steady rainfall starting this morning and continuing well into Friday night. Cool air will be a feature of this low, so much of the rain will be a windy, cold rain. This does not favor much in the way of convective activity, which will limit rainfall rates. Any upper level instability will remain over VA and NC, with little getting any further north than the DC Metro. Given the lack of instability and ongoing longer-term drought, and the eastward shift in the axis of heaviest rainfall in the comma-head/cold sector of the storm, the inherited Marginal Risk was trimmed out of PA and NJ due to lack of instability, as well as trimmed out of southwest VA and western NC. The heaviest rain is currently expected along and east of the I-95 corridor, so it's in this area where the Marginal remains in place. Wegman Day 2 Valid 12Z Sat Apr 12 2025 - 12Z Sun Apr 13 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Sun Apr 13 2025 - 12Z Mon Apr 14 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7d_yKLBigPV54EdyG3-G9UDj0jBT6NQiVHzk0nmUMh2U= TEzTqdRiIXDtGKA4-IxLULxwAR4DmEQfmvyXg_-L9SuRzE4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7d_yKLBigPV54EdyG3-G9UDj0jBT6NQiVHzk0nmUMh2U= TEzTqdRiIXDtGKA4-IxLULxwAR4DmEQfmvyXg_-L9u5_BDc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7d_yKLBigPV54EdyG3-G9UDj0jBT6NQiVHzk0nmUMh2U= TEzTqdRiIXDtGKA4-IxLULxwAR4DmEQfmvyXg_-LzF3grsc$=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) .