Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Oct 29 2025 19:10:16 FOUS30 KWBC 291910 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 310 PM EDT Wed Oct 29 2025 Day 1 Valid 16Z 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... 16Z Update: Main change was removal of the valley areas of eastern TN where an areal min in QPF is forecast across all guidance leading to limited flash flood concerns. Remainder of the forecast is on track with the primary maxima still situated in the Central and Southern Appalachians and neighboring Blue Ridge in VA. Neighborhood probs from the latest 12z HREF were indicative of some >3" maxima situated over the Northern Neck of VA with probabilities uptick to 25-50% in-of the Blue Ridge extension just east of I-81. This makes sense synoptically with the increasing upslope component initiating overnight into the end of the period with a modest instability regime developing along the terrain and points east thanks to the projected theta_E advection pattern materializing as the ULL pivots eastward and we reside in persistent onshore fetch from the Atlantic. Thanks to dry antecedent conditions leading into the period, the setup is curbed to be more in line with a MRGL risk threshold, thus maintained general continuity outside the small change in TN and the western fringes of the risk area across central TN and KY. 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. HREF neighborhood probs for >2" are relatively high in-of the Blue Ridge from Virginia down into the western Carolinas (60-90%) with a vast majority of the rain 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 leading to a greater potential for that low- topped convection to impact these zones. A Marginal Risk area remains in effect for this part of the nation. Campbell/Kleebauer Day 2 Valid 12Z Thu Oct 30 2025 - 12Z Fri Oct 31 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MID ATLANTIC AND NORTHEAST... 20Z Update: The current pattern remains consistent within guidance with the mean QPF maxima between 1.25-2.5", local to 3" forecast over Southeast PA up through parts of NJ, NYC metro, western LI, and southwest CT. Main adjustment from previous issuance is the expansion of the MRGL risk down through southeast PA to include more of the Philadelphia metro and surrounding suburbs. Despite antecedent dry soils overall across the area, high urban density coupled with anticipation of rates >1"/hr at times will promote a greater threat for run off with some isolated flash flood concerns in those areas comprised of mostly an urban footprint. 12z HREF probs are generally elevated (50-90%) for areas of >2" over much of southeast and eastern PA into the northern half of NJ, the most likely location for flash flood prospects considering the instability presence coupling with the well-above normal PWATs forecast over the region. In coordination with the local Mount Holly WFO covering the area of interest, a MRGL risk expansion was made to account for the threat tomorrow morning and afternoon. Kleebauer ...Previous Discussion.. This system is forecast to track to the northeast as the associated surface low strengthens over the Mid-Atlantic onward to the Northeast. Heavy rain will accompany the low and overspread the region. 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 Pennsylvania up through New Jersey, New York City metro, and western Long Island to about the I-95 corridor in Connecticut. A Marginal Risk for excessive rainfall and isolated flash flood concerns in that urbanized corridor of the Northeastern U.S. remains for this period. Campbell/Kleebauer Day 3 Valid 12Z Fri Oct 31 2025 - 12Z Sat Nov 01 2025 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR NORTHWESTERN WASHINGTON STATE... 20Z Update: A relatively stout atmospheric river will setup across the PAC Northwest with an advection of high (>750 Kg/ms) into the region beginning Friday afternoon, carrying through the late evening Friday into Saturday. Precip rates between 0.5-0.75"/hr are forecast in-of the Olympics and surrounding locales during the height of the event with a general 0.25-0.5"/hr rates likely on average during the period of impact. This will produce rainfall totals between 1-3" with upwards of 4-5" in the higher terrain focused in the Olympics where the greatest upslope pattern will occur with the higher rates progged. Areas along the western slopes of the northern Cascades will also see some enhancement of precip for a period on Friday evening as the IVT pulse protrudes inland and allows for a focused secondary maxima in the aforementioned area. Forecast rivers in this area are expected to rise into action stage due to the incoming rainfall, so there's a low end threat of localized flooding within the confines of these river locations.=20 Considering the consistency within guidance on totals and expectation for some enhanced rates to generate river rises and minor flooding, a MRGL risk was maintained over the Olympic Peninsula over into the western side of the northern Cascades.=20 Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4cmn0ef_9PUycApvG_HIA_ooS3kdDy6S66IH1steWFA6= ccaj_g1wEJx9mifTK5WCUSoGnAPW7n61IgSKuakNjO6zo-w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4cmn0ef_9PUycApvG_HIA_ooS3kdDy6S66IH1steWFA6= ccaj_g1wEJx9mifTK5WCUSoGnAPW7n61IgSKuakN5DgxO0Q$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4cmn0ef_9PUycApvG_HIA_ooS3kdDy6S66IH1steWFA6= ccaj_g1wEJx9mifTK5WCUSoGnAPW7n61IgSKuakNyxdSCO0$=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) .