Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Oct 04 2025 00:56:32 FOUS30 KWBC 040056 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 856 PM EDT Fri Oct 3 2025 Day 1 Valid 01Z Sat Oct 04 2025 - 12Z Sat Oct 04 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF EASTERN FLORIDA AND THE INTERMOUNTAIN WEST... ....Florida's East Coast... For the 03/01Z Update, made few changes to either Marginal Risk area. The northern portion of the Marginal Risk area in Florida was removed for the duration of the overnight hours as drier air filtered in from the north during the day. The respite should be short-lived. Farther south...maintained the Marginal Risk area where the moisture was deeper and radar still showed some showers and thunderstorms poised to move inland with some potential to bring brief heavy rainfall to highly urbanized areas in the short=20 term. Across the West...Late afternoon/early evening water vapor satellite imagery showed a shortwave trough making its was across the southern portion of the Marginal risk area. That was helping focus some generally light showers. Maintained the Marginal risk area given recent heavy rainfall over portions of the Great Basin=20 will likely have primed surfaces for runoff from additional=20 precipitation. Burn scars continue to be of concern this evening. Also noted that the 18Z HREF EAS exceedance probabilities continued to show a low-end risk of 1- and 3-hourly flash flood guidance being exceeded into the overnight hours over northern/central=20 Nevada where PWATs will be between 2-3 standard deviations above=20 normal. Bann Day 2 Valid 12Z Sat Oct 04 2025 - 12Z Sun Oct 05 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF FLORIDA'S EAST COAST... 20Z Update... The Marginal Risk was removed from southeastern Louisiana. Consensus of the 12Z HREF and 06Z RRFS showed their higher probabilities for onshore heavy amounts that are associated with a slow-moving wave remaining confined to the immediate coast and away from the more vulnerable I-10 corridor. Should the models trend back to the north, a Marginal Risk may be reintroduced, but for now the area has been removed from the outlook. For the Florida East Coast, the signal for widespread showers and storms, with locally heavy amounts remain. Models have been generally trending lighter with their QPF. However, with the HREF still showing some higher probabilities for amounts over 3 inches, left the Slight Risk centered along the Space/Treasure coasts in place for now. Also extended the Marginal Risk further south into the Miami metro, where the hi-res ensembles also show some higher for amounts over 3 inches. Previous Discussion... ....Florida's East Coast... Thunderstorms are expected to continue to develop along the inverted trough axis oriented north-south along Florida's east coast on Saturday. Moisture will lift north along with the mid- level disturbance. The inherited slight and marginal risk areas were maintained due to a mostly consistent signal for excessive rainfall over the east central coast. Ensemble exceedance probabilities of 2 inches are between 5-10% across the marginal risk area. 48 hour totals between 3-5 inches (local 6") will likely make overcoming flash flood guidance a bit easier. Pereira/Kebede Day 3 Valid 12Z Sun Oct 05 2025 - 12Z Mon Oct 06 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CENTRAL GULF COAST AND THE SOUTHEAST COAST... 20Z Update... No significant changes were made to the previous outlook. Previous Discussion... ....Central Gulf Coast... The mid-level disturbance continues propagating westward toward the positively tilted upper trough centered over the West on Sunday. Thus, the heavy rainfall threat will likely bleed over from Saturday evening into Sunday morning for portions of the Central Gulf Coast, before dissipating beneath diminished support aloft. PWATs of 2-2.5" and instability between 500-1000 J/Kg MUCAPE could churn out rain rates between 1-1.5"/hr Saturday morning into afternoon. Ensemble exceedance probabilities of 2 inches are between 5-15% along the far southeastern Louisiana to Florida panhandle corridor, which supports the marginal risk area in place. ....Southeast Coast... Inverted troughing continues along the Florida/Southeast Coast through the latter part of this weekend. Anomalous moisture (2-3 stndv) will continue interacting with the surface boundary to generate scattered to isolated thunderstorms across the Florida/Georgia coast. Rainfall totals of 1-3" are likely along the Florida/Georgia/South Carolina coast on Saturday. The latest guidance has trended away from tropical moisture making its way inland, therefore a marginal risk was maintained for much of the Southeast Coast. Pereira/Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7q1YusVS2TQk_bBeEGA09DfUHFZVKq_Jy_wy8qjwKM0C= z4NJoGOVcYBasMjuB09LIxQl-P64D7tOb09edAZNsIPvlCM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7q1YusVS2TQk_bBeEGA09DfUHFZVKq_Jy_wy8qjwKM0C= z4NJoGOVcYBasMjuB09LIxQl-P64D7tOb09edAZNPekqucc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7q1YusVS2TQk_bBeEGA09DfUHFZVKq_Jy_wy8qjwKM0C= z4NJoGOVcYBasMjuB09LIxQl-P64D7tOb09edAZNI9JBRVY$=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) .