Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Oct 28 2025 23:57:10 FOUS30 KWBC 282352 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 752 PM EDT Tue Oct 28 2025 Day 1 Valid 01Z Wed Oct 29 2025 - 12Z Wed Oct 29 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Hurley Day 2 Valid 12Z Wed Oct 29 2025 - 12Z Thu Oct 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN AND CENTRAL APPALACHIANS AND SURROUNDING PORTIONS OF THE OHIO/TENNESSEE VALLEYS... 20Z Update: The prior forecast remains on track with little deviation in the QPF distribution focused over the Central and Southern Apps into the Ohio Valley and Mid Atlantic. 12z HREF neighborhood probs for >2" are relatively high in-of the Blue Ridge from VA down into the western Carolinas (60-90%) with a vast majority of the precip coming from shallow convective processes focused within the terrain. Large scale forcing across the aforementioned areas will be the primary driver for the heavy rain scenario, however a tongue of elevated theta_E is expected to advect off the Atlantic into the Central Apps/Blue Ridge by the end of the forecast cycle leading to a greater potential for that low- topped convection to impact these zones. That's likely the case for the prob fields being more elevated in these zones just due to a more favorable environment coincident for those convective schemes and subsequent heavier rainfall footprint. In any case, the setup still favors a more modest MRGL risk prospect for flash flooding as drier soils should initially help curb some of the threat with a more localized focus of impact. Thus, the MRGL risk was maintained with only some minor adjustments to reflect the QPF max/min distribution spatially. Kleebauer ...Previous Discussion.. Rainfall is expected to overspread the Tennessee/Ohio Valley with anomalous low- level moisture transport driving east-southeast moisture transport into the Southern/Central Appalachians as a closed upper low swivels from the Mid-South to the Ohio Valley. Much of this part of the country will experience beneficial moisture; however there will be embedded locations that have the potential for intra-hour rates of 1-1.5 inches/hour that could result in localized flash flooding. This is despite limited instability (similar to Day 2 across the Mid- South), as the dynamics of the closed low (notable PV anomaly with enhanced divergence aloft via left exit region of ~130 kt jet streak @ 250 mb) may result in localized 2" exceedance in the Ohio/Tennessee Valley (with terrain forcing primarily driving any localized 2" exceedance along/east of the Southern/Central Appalachians). Campbell/Churchill Day 3 Valid 12Z Thu Oct 30 2025 - 12Z Fri Oct 31 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE SOUTHERN PORTION OF THE NORTHEAST... 20Z Update: Our system will navigate to the northeast with a strengthening surface low moving through the interior Mid Atlantic, eventually sights on the Northeast by the end of the forecast cycle. Heaviest rainfall will likely occur across southeastern PA up through northern and central NJ, southern NY state (NYC/LI included), into southern New England. The best threat for convective enhancement leading to better rates >1"/hr and some minor training off steady southeast flow off the Atlantic will occur from southeast PA up through NJ, NYC metro, and western LI to about the I-95 corridor in CT. This area has a favorable FFG exceedance marker due to the widespread urbanization footprint leading to run off capabilities. The forward propagation of the precip will likely mitigate the worst impact scenarios, but still resides within the lower to middle threshold of the MRGL risk category for flash flood concerns as we add that more favorable convective element. PWATs between 2-3 deviations above normal also enhance the probability for more efficient rainfall prospects, so even with a window only 6-9 hrs. for general impact, this would still be enough for perhaps some isolated flash flood concerns in that urbanized corridor of the Northeastern U.S. The MRGL was adjusted to reflect the latest QPF trends with the biggest expansion occurring along the I-95 corridor in southwest CT. Kleebauer ...Previous Discussion.. The system mentioned for the day 2 period will continue to advance up the Eastern Seaboard directing widespread rain to the Northeast. Guidance is suggesting the highest rainfall accumulations will focus over northern New Jersey and southeast New York where WPC has areal averages of 1.5-2.5 inches forecast for this period. This part of the region is where the best potential for reaching or exceeding local FFG guidance so a Marginal Risk area remains in effect for portions of New Jersey, Pennsylvania, New York, and Connecticut. Campbell Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-_Fzal8e2AcIYGHTO2Ft5cD3VaDmS9MPgwauA3-CQFai= oZsYUM-zu5BD7aiEx9iUJQEmSD1OLzaT-tnkeyoBdj7INTA$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-_Fzal8e2AcIYGHTO2Ft5cD3VaDmS9MPgwauA3-CQFai= oZsYUM-zu5BD7aiEx9iUJQEmSD1OLzaT-tnkeyoBVc92NWo$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-_Fzal8e2AcIYGHTO2Ft5cD3VaDmS9MPgwauA3-CQFai= oZsYUM-zu5BD7aiEx9iUJQEmSD1OLzaT-tnkeyoB2pzYYj4$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .