Subj : HVYRAIN: Excessive Rainfa To : All From : Mike Powell Date : Thu Oct 02 2025 09:43:46 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 Rockies. Diffluence will spread across the aforementioned areas throughout the day on Friday. At the surface, a low pressure system will propagate across the interior West, while anomalous moisture (3-4 stndv PWATs) streams in behind the preceding cold front. Scattered to isolated thunderstorms may develop and produce isolated instances of excessive rainfall and flash flooding. Upslope enhancement across the Sierra could produce heavier rainfall totals than what are currently forecast. EAS probabilities of 24 hour qpf exceeding 1 inch are over 40% in the Sierra and between 15-40% in the Great Basin. Therefore, burn scars over 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 boundary draped along the eastern coast will focus PWATs of around 2" in that area where MUCAPE between 500-1000 J/Kg will also likely produce high rain rates. Neighborhood probabilities of exceeding 5" in 24 hours are between 40-90% from near Miami metro up through 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 lifting north on Friday. The excessive rainfall threat bleeds into Friday from Thursday as thunderstorms weaken and spread from the Great Basin into the Northern Rockies by Friday afternoon. Instability and moisture will be relatively modest (100-200 J/Kg MUCAPE) (0.5-0.9"). Ensemble exceedance probabilities of 1" are between 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. Another inverted surface trough may develop along the state's east coast and focus convection along the convergence zone. Ensemble exceedance probabilities of 2" are between 5-15% along the 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 moisture into the region on Saturday. Convection should fire along 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 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 should flow up the Florida Peninsula into far southeastern Georgia where PWAT's of over 2" and an inverted surface trough could combine to produce thunderstorms capable of generating 0.75-1"/hr rain rates. Ensemble exceedance probabilities of 2" are between 5-15% along Florida's east coast into southeastern Georgia. Kebede $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) .