Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Sep 29 2025 08:30:31 FOUS30 KWBC 290830 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 430 AM EDT Mon Sep 29 2025 Day 1 Valid 01Z Mon Sep 29 2025 - 12Z Mon Sep 29 2025 ....THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 NORTHERN CALIFORNIA, SOUTHWESTERN OREGON, THE GREAT BASIN, SOUTH- CENTRAL NEW MEXICO AND THE SOUTHEAST... ....Carolinas... Moisture from tropical storm Imelda is expected to continue=20 streaming into the Southeast Coast today. A surface front draped=20 off the coast should provide forcing for thunderstorm development=20 beginning this morning. Convective bands may work their way into a=20 moisture rich environment in the Carolinas, where PWATs will be=20 between 1.5-2.25in.. MUCAPE between 250-500 J/Kg will spread=20 inland throughout the day, but the greatest convective potential=20 will be within the bands that propagate inland through North=20 Carolina this morning and afternoon. Neighborhood probabilities of=20 exceeding 2 inches of rainfall in 24 hours are between 15-30% over=20 parts of western and central North Carolina today. Despite the presence of deep tropical moisture, much of the convection and heaviest rainfall associated with Imelda should stay offshore closer to Imelda and the draped front. ....Northern California/Great Basin... A deep upper low centered over the Gulf of Alaska will send waves of low pressure into the West Coast over the next couple of days.=20 A strong cold front may bring heavy rainfall to portions of=20 Northern California up into southern Oregon and the Great Basin=20 today. A weak instability gradient will develop ahead of the front=20 this afternoon and during peak heating. The 00z HREF suggest up to=20 0.25in./hr. rates across the coastal ranges, southern Cascades and=20 northern Sierra, with potential for upslope enhancement across=20 windward facing slopes.=20 EAS 24 hour 1 inch exceedance probabilities are over 45% along the coast and southern Cascades, while a more modest 5-15% chance=20 remains over the Great Basin. There's a steep drop off in=20 probabilities once you get into the 2 inch exceedance range. ....South-central New Mexico... There continues to be a signal for heavy rainfall over much of the Sacramento Mountains, where instability (500-1000 J/Kg MLCAPE) could support thunderstorm development and propagation into the mountains early this evening. Much of the state has already received over a half inch of rainfall in the past 24 hours with pockets of 2 inch amounts present including within the Sacramento Mountains. This may contribute to susceptibility of soils to runoff from additional rain. Burn Scars such as the Ft. Stanton Piles prescribed burn area are especially susceptible to flash flooding. Kebede Day 2 Valid 12Z Mon Sep 29 2025 - 12Z Tue Sep 30 2025 ....THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GREAT BASIN AND NORTHERN ROCKIES... The marginal risk area inherited from the previous cycle was mostly maintained with an expansion south into central Utah due to trends in the guidance. The cold front responsible for heavy rainfall potential in northern California on Monday will propagate through the Great Basin and Northern Rockies on Tuesday, focusing additional instability and moisture along its convergence zone. Ensemble exceedance probabilities of 0.5 inches in 24 hours are=20 between 5-25% over parts of northeastern Nevada, northern Utah, southeastern Idaho and western Wyoming. The progressive nature of the front should mitigate flash flooding concerns. Kebede Day 3 Valid 12Z Tue Sep 30 2025 - 12Z Wed Oct 01 2025 ....THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE OLYMPIC PENINSULA... A shortwave propagating through the southern periphery of the Gulf of Alaska low will phase with it and move just off of the British Columbia Coast by Wednesday. This new system will send a cold=20 front into the Pacific Northwest. The proximity of the upper low and associated vorticity lobes should destabilize the environment=20 (100-300 J/Kg MUCAPE) enough to support isolated thunderstorm=20 activity. Favorable RER dynamics and mid-level moisture=20 advection should support efficient rain rates especially over the=20 Olympic Mountains. ECENS 24 hour exceedance probabilities of 2=20 inches is between 20-40% for much of the area. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!982xJkrpFgC71mUHP6iNhc8sD5AKYCZ6MNJsaAZUo7UN= 3yD6iSxI4FKSW_naOhtnUdVwHmS5qZf5nOsyJuDPIQqfngc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!982xJkrpFgC71mUHP6iNhc8sD5AKYCZ6MNJsaAZUo7UN= 3yD6iSxI4FKSW_naOhtnUdVwHmS5qZf5nOsyJuDPxFFDGMY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!982xJkrpFgC71mUHP6iNhc8sD5AKYCZ6MNJsaAZUo7UN= 3yD6iSxI4FKSW_naOhtnUdVwHmS5qZf5nOsyJuDPTRCoIrA$=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) .