Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 30 2025 08:16:20 FOUS30 KWBC 300816 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 416 AM EDT Tue Sep 30 2025 Day 1 Valid 01Z Tue Sep 30 2025 - 12Z Tue Sep 30 2025 ....THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE OLYMPIC MOUNTAINS, GREAT BASIN AND NORTHERN ROCKIES... ....Great Basin/Northern Rockies... A deep upper low off the British Columbia Coast will send=20 shortwave energy through the Northwest today. A progressive cold=20 front will focus showers and thunderstorms over portions of the=20 Great Basin from northeast Nevada to western Montana/northern=20 Idaho. MUCAPE values between 100-500J/Kg and PWATs of 0.5-1in.=20 could produce excessive rainfall through this afternoon. This will=20 be especially true over portions of eastern Nevada into northern=20 Utah where 24 hour 1 inch exceedance probabilities are between=20 20-45%. ....Olympics... The occluded parent low will direct anomalous Pacific moisture at=20 the Olympic coast beginning this afternoon. Some weak instability=20 (<200J/Kg MUCAPE) and PWAT's around 1 inch could produce some cells capable of generating efficient rain rates, especially within the=20 windward side of the Olympics. IVT values between 500-700Kg/ms support the excessive rainfall threat with isolated instances of flash flooding. Kebede Day 2 Valid 12Z Tue Sep 30 2025 - 12Z Wed Oct 01 2025 ....THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE OLYMPIC MOUNTAINS... The excessive rainfall threat over the Olympics bleeds into Wednesday as the upper low arrives off the coast of the Pacific Northwest. A jetstreak aloft with MUCAPE around 150J/Kg Wednesday morning could support some weak convection into the Olympics. Unlike on day 1, maximum IVT values will remain offshore with 1=20 inch PWATs arriving early Thursday morning. Canadian and Euro ensemble 2 inch exceedance probabilities are between 40-60% while=20 the GEFS 1 inch probabilities are around an inch.=20 Kebede Day 3 Valid 12Z Wed Oct 01 2025 - 12Z Thu Oct 02 2025 ....THERE'S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE GREAT BASIN AND EASTERN FLORIDA... ....Great Basin... The upper low is expected to dig into the West Coast on Thursday directing diffluent flow and left exit region jet dynamics into the Great Basin. Weak instability (100-200J/Kg MUCAPE) along a developing cold front could generate thunderstorms capable of=20 producing some isolated flash flooding, especially over parts of=20 the Great Basin that received rainfall on Tuesday. ....Eastern Florida... An upper trough in the Southeast will direct embedded vorticity=20 into the Florida peninsula on Thursday. An upper ridge centered=20 over the West Atlantic will advect tropical moisture (PWATs=20 between 1.5-2in.) into eastern Florida, where it'll interact with=20 an inverted trough along the coast. Multiple rounds of short fused convection will proliferate from the central Gulf across the=20 Florida Peninsula throughout the day with onshore flow into eastern Florida producing isolated instances of flash flooding.=20 Probabilities of 24 hour qpf exceeding 1 inch is between 15-30%=20 across eastern Florida. Urban areas are especially susceptible to=20 flash flooding. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-7W00vFpJiSOKioLBq0E7XQg4GyhtrVCynVHNHK-jESU= GZHX7ffdnWMmniIt1HcA6kg8Ll8VnxlpAn-NAy5YOj_uWVw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-7W00vFpJiSOKioLBq0E7XQg4GyhtrVCynVHNHK-jESU= GZHX7ffdnWMmniIt1HcA6kg8Ll8VnxlpAn-NAy5YLkFqa1Q$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-7W00vFpJiSOKioLBq0E7XQg4GyhtrVCynVHNHK-jESU= GZHX7ffdnWMmniIt1HcA6kg8Ll8VnxlpAn-NAy5YE8W9YH8$=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) .