Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 30 2025 19:45:17 FOUS30 KWBC 301945 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 345 PM EDT Thu Oct 30 2025 Day 1 Valid 16Z Thu Oct 30 2025 - 12Z Fri Oct 31 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE NORTHEAST MID-ATLANTIC AND SOUTHERN NEW ENGLAND... A strong deep layer trough and associated closed low will continue to gradually take on a negative tilt today through tonight as the energy pivots gradually out of the Mid-Atlantic region and into the Northeast. Strong DPVA coupled with enhanced low-level moisture transport/convergence and modest instability around the northeast flank of a strengthening and occluded low center will drive bands of heavy showers and a few thunderstorms up across portions of eastern PA, NJ, southeast NY, and adjacent areas of southern New England. The short-term concerns will be mainly to eastern PA and NJ as a ribbon of modest instability with MUCAPE values of ~500 J/kg nose up across the region with a strongly forced environment. The 12Z HREF and 06Z REFS solutions suggest some linearly oriented bands of convection will be possible with rainfall rates potentially up to 1 inch/hour before the frontal occlusion crosses the region. However, areas of northern NJ, far southeast NY (including the greater NYC metro area) and into adjacent areas of southern New England (CT/RI) will see some potential for some brief convective cell-training concerns this evening as the low-level Atlantic moisture transport (aided by 925/850 mb flow of 40 to 50 kts) becomes increasingly convergent/focused near a developing triple point low as the primary low advances well inland. Very modest instability will keep the rainfall rates somewhat subdued, but the level of dynamic jet-aided forcing/ascent through the column and the moisture transport may support some spotty 1 to 1.5 inch/hour rainfall rates. Localized storm total amounts of 2 to 4 inches will be possible where any cell-training ends up occurring, but with the dry antecedent conditions, any flash flooding concerns will be isolated and mainly confined to the urbanized corridors closer to I-95. As such, the Marginal Risk area is maintained and just locally tweaked to account for the latest radar trends and 12Z hires CAM solutions. Orrison Day 2 Valid 12Z Fri Oct 31 2025 - 12Z Sat Nov 01 2025 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR WESTERN WASHINGTON... 2030Z Update... Generally no changes to the previous thinking. The latest guidance continues to support atmospheric river conditions arriving across western WA this period which will drive heavy rainfall into the coastal ranges and the windward slopes of the Cascades. Snow levels will be rather high, some there will be heavier rainfall amounts materializing at some of the higher elevations which as previously mentioned may reach as high as 3 to 5 inches for the period. Made only cosmetic changes to the Marginal Risk area for this update. Orrison Previous discussion... A modestly strong atmospheric river will setup across the Pacific Northwest with an advection of high IVT (>750 Kg/ms) into the=20 region beginning Friday afternoon, carrying through the late=20 evening Friday into Saturday. Inflow at 850 hPa approaches 50 kts=20 out of the southwest while precipitable water values in the coastal ranges rise into the 1.25-1.5" range. MU CAPE is forecast to=20 remain weak, under 250 J/kg. Precip rates should rise to between=20 0.5-0.75"/hr during the peak of the heavy rainfall, producing local amounts of 3-5" in the higher terrain of western WA, which would=20 be particularly challenging for the Skokomish river. Considering=20 the consistency within guidance on totals and expectation for some=20 enhanced rates to generate river rises and minor flooding, a=20 Marginal Risk was maintained, with some expansion to the south to=20 account for the wetter 00z UKMET solution. Roth Day 3 Valid 12Z Sat Nov 01 2025 - 12Z Sun Nov 02 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Roth/Orrison Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!709h4ElSLaQWf_AVP726U-AkrgEET3OqvO208qJRUTEE= xdTcT8Q1y8Yivvom74iAl6it_5-WOXh5cZ2QzEX36Sjv7sQ$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!709h4ElSLaQWf_AVP726U-AkrgEET3OqvO208qJRUTEE= xdTcT8Q1y8Yivvom74iAl6it_5-WOXh5cZ2QzEX3goLC3ik$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!709h4ElSLaQWf_AVP726U-AkrgEET3OqvO208qJRUTEE= xdTcT8Q1y8Yivvom74iAl6it_5-WOXh5cZ2QzEX3uJt9i14$=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) .