Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 17 2025 01:00:24 FOUS30 KWBC 170100 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 900 PM EDT Sun Mar 16 2025 Day 1 Valid 01Z Mon Mar 17 2025 - 12Z Mon Mar 17 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA... ....East Coast... Scattered thunderstorms were ongoing at 00Z from central New York into far western Virginia, located out ahead of the advancing northern portion of a mid-upper level trough seen on water vapor=20 imagery over southern Ontario. A second axis of scattered thunderstorms was noted from the DelMarVa Peninsula into south- central Virginia, central North Carolina and the Southeast coast...out ahead of an advancing southern portion of the mid-upper level trough over the east-central Gulf Coast...with a relative=20 break between the northern and southern convective areas. MLCAPE=20 was approximately 500 to 1000 J/kg from eastern Pennsylvania into=20 the eastern Carolinas.=20 Mean steering flow was from the southwest with 0-6 km layer winds at 50-60 kt, but areas of training were occurring within low level axes of convergence, aligned with the mean steering flow,=20 supporting 1-2 in/hr rainfall rates at times. Of greatest concern=20 in the short term was an area of expanding thunderstorm intensity=20 in the vicinity of the Virginia/North Carolina border at 00Z which was along a pre-frontal, low level convergence axis that extended=20 from eastern North Carolina into southeastern Virginia and the=20 southern DelMarVa Peninsula. Slow movement of this convergence=20 axis, coupled with strengthening right-entrance region ascent=20 related to an upper level jet max over the northern Mid-Atlantic=20 region should provide for a prolonged period of heavy rain with=20 hourly rates between 1-2 inches at times, leading to additional 3-4 inch totals (at least locally). The Slight Risk introduced Sunday=20 afternoon remains centered over southeastern Virginia where a=20 cluster of urban influences result in a greater potential for rapid rises of water due to heavy rainfall, compared to locations north=20 (DelMarVa into southeastern New Jersey) and south (eastern North=20 Carolina).=20 Elsewhere, similar areas of training (but with lower hourly rainfall totals, capped near 1 inch) are expected into portions of Long Island and southern New England later tonight where 2 to 3 (perhaps up to 4 inches) may occur through 12Z Monday. ....West Coast... The anomalous moisture plume (+1 to +2 standardized PWAT anomalies) which has been focused into northern California and southwestern Oregon over the past 12-24 hours has begun to shift south since 18-21Z=20 Sunday. Various observation networks showed that rainfall totals=20 over the past 24 hours ranged from 3 to perhaps as high as 10=20 inches along the southern Oregon Coastal Ranges. As an upper trough axis over the eastern Pacific continues to advances southeastward=20 tonight, the low level moisture axis will continue to weaken and drop south ahead of the associated cold front currently located across the northern California coast. The greatest additional=20 rainfall totals are expected in the upslope ranges of the northern=20 Sierra Nevada where an additional 1 to 3 inches may fall through=20 12Z, below crashing snow levels behind the cold front. Back to the west along the Coastal Ranges, PWATs and low level winds will be much weaker compared to earlier on Sunday but steep mid-level lapse rates will allow for thunderstorms with brief/intense rainfall to become scattered and move onshore ahead of an approaching surface low and trailing trough axis. Occasional rain rates in excess of 0.5 in/hr will be possible both along the Coastal Ranges and into the Sierra Nevada, but with additional rainfall totals along the coast being limited to 1 to 2 inches at most through 12Z Monday. Any areas of existing/ongoing=20 flooding could be exacerbated with additional, locally heavy,=20 rainfall.=20 Otto Day 2 Valid 12Z Mon Mar 17 2025 - 12Z Tue Mar 18 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman Day 3 Valid 12Z Tue Mar 18 2025 - 12Z Wed Mar 19 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!82okxitDzwzy9HR62iMx4n9XAqaUu1F1coBOmfltiscw= TbXEZA-BmS-1TOo8OqpYu3tjUOLqnGqjtaH8TKzHo39iHks$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!82okxitDzwzy9HR62iMx4n9XAqaUu1F1coBOmfltiscw= TbXEZA-BmS-1TOo8OqpYu3tjUOLqnGqjtaH8TKzHPvfqFPg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!82okxitDzwzy9HR62iMx4n9XAqaUu1F1coBOmfltiscw= TbXEZA-BmS-1TOo8OqpYu3tjUOLqnGqjtaH8TKzHh35a9xk$=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) .