Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 30 2025 00:56:05 FOUS30 KWBC 300055 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 855 PM EDT Wed Oct 29 2025 Day 1 Valid 01Z Thu Oct 30 2025 - 12Z Thu Oct 30 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS INTERIOR PORTIONS OF THE MID ATLANTIC, INCLUDING THE SHENANDOAH VALLEY AND BLUE RIDGE... 0100Z Update: Low-end Marginal Risk area was trimmed considerably based on the latest observational and short-range guidance trends. Deep-layer instability is quite meager, averaging 100 to maybe 500 J/Kg after midnight within the outlook area. 18Z HREF probabilities of QPF exceeding 3" through 12Z are highest within the Marginal Risk area, peaking between 50-60%. However despite the favorable=20 (albeit transient) deep-layer synoptic support, the lack of instability and anomalous moisture (PWs only 1 to maybe 1.25") will again lead to a low-end Marginal Risk outlook.=20 Hurley 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. 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. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4FfgSqDkW6plNVUuiRmYkqSbuNluXKtJmRRiDSxO4-mq= krZl4IqybtZzDvS-hNxSl8twRJ7swo-v8-tJCnj6TANAN4c$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4FfgSqDkW6plNVUuiRmYkqSbuNluXKtJmRRiDSxO4-mq= krZl4IqybtZzDvS-hNxSl8twRJ7swo-v8-tJCnj6Be7jYQ4$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4FfgSqDkW6plNVUuiRmYkqSbuNluXKtJmRRiDSxO4-mq= krZl4IqybtZzDvS-hNxSl8twRJ7swo-v8-tJCnj6mTux1AY$=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) .