Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 02 2025 08:28:43 FOUS30 KWBC 020828 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 428 AM EDT Thu Oct 2 2025 Day 1 Valid 12Z Thu Oct 02 2025 - 12Z Fri Oct 03 2025 ....THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SIERRA, GREAT BASIN AND EASTERN FLORIDA... ....Sierra/Great Basin... An upper low will dig into the West Coast while sending streams of vorticity into the Sierra Nevada, Great Basin and Northern=20 Rockies. Diffluence will spread across the aforementioned areas=20 throughout the day on Friday. At the surface, a low pressure system will propagate across the interior West, while anomalous moisture=20 (3-4 stndv PWATs) streams in behind the preceding cold front.=20 Scattered to isolated thunderstorms may develop and produce=20 isolated instances of excessive rainfall and flash flooding.=20 Upslope enhancement across the Sierra could produce heavier=20 rainfall totals than what are currently forecast. EAS probabilities of 24 hour qpf exceeding 1 inch are over 40% in the Sierra and=20 between 15-40% in the Great Basin. Therefore, burn scars over=20 central and southern Idaho are at risk of flash flooding today. ....Eastern Florida... Moist easterly flow into a surface front oriented north-south will produce scattered convection across Florida today. The surface=20 boundary draped along the eastern coast will focus PWATs of around=20 2" in that area where MUCAPE between 500-1000 J/Kg will also likely produce high rain rates. Neighborhood probabilities of exceeding=20 5" in 24 hours are between 40-90% from near Miami metro up through=20 Melbourne and Orlando. Kebede Day 2 Valid 12Z Fri Oct 03 2025 - 12Z Sat Oct 04 2025 ....THERE'S A MARGINAL RISK FOR PORTIONS OF THE GREAT BASIN AND EASTERN FLORIDA... ....Great Basin... The upper trough propagates through the Great Basin and begins=20 lifting north on Friday. The excessive rainfall threat bleeds into Friday from Thursday as thunderstorms weaken and spread from the=20 Great Basin into the Northern Rockies by Friday afternoon. Instability and moisture will be relatively modest (100-200 J/Kg MUCAPE)=20 (0.5-0.9"). Ensemble exceedance probabilities of 1" are between=20 10-20% over northern Nevada with 2 day totals potentially eclipsing 2" in some places. ....Eastern Florida... Moisture advection into Florida increases on Friday as a mid-level circulation embedded within a broader upper ridge continues to direct moisture and instability into the state's east coast.=20 Another inverted surface trough may develop along the state's east coast and focus convection along the convergence zone. Ensemble=20 exceedance probabilities of 2" are between 5-15% along the=20 immediate coast, while first guess fields support the marginal with 5% flash flood probabilities. Kebede Day 3 Valid 12Z Sat Oct 04 2025 - 12Z Sun Oct 05 2025 ....THERE'S A MARGINAL RISK FOR PORTIONS OF SOUTHEAST LOUISIANA AND EASTERN FLORIDA INTO FAR SOUTHEASTERN GEORGIA... ....Central Gulf Coast... Mid-level vorticity swirling over the Central Gulf Coast will generate instability and pull an increasing amount of Gulf=20 moisture into the region on Saturday. Convection should fire along=20 a coastal convergence zone that develops and diurnal heating should enhance afternoon/evening storms along that boundary. PWATs will likely be over 2" with MUCAPE between 500-750 J/Kg. Ensemble exceedance probabilities of 2" are between 15-30% for much of southeast=20 Louisiana. ....Eastern Florida/Southeastern Georgia... Tropical moisture associated with Imelda will continue flowing into Florida due to and upper ridge over the East Coast and embedded troughing over Florida and the Gulf. A modest instability plume=20 should flow up the Florida Peninsula into far southeastern Georgia=20 where PWAT's of over 2" and an inverted surface trough could combine to produce thunderstorms capable of generating 0.75-1"/hr=20 rain rates. Ensemble exceedance probabilities of 2" are between=20 5-15% along Florida's east coast into southeastern Georgia. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5QMibcjbv8UIoTFzL7jA06j0OeJ8rgJX3NQrBodnUdto= 0N3yKv--zID7olPZgjbAEjsDg2dbjEODBS5D83_TzDyC4E0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5QMibcjbv8UIoTFzL7jA06j0OeJ8rgJX3NQrBodnUdto= 0N3yKv--zID7olPZgjbAEjsDg2dbjEODBS5D83_T_tNI8og$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5QMibcjbv8UIoTFzL7jA06j0OeJ8rgJX3NQrBodnUdto= 0N3yKv--zID7olPZgjbAEjsDg2dbjEODBS5D83_TBlxoeD8$=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) .