Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 27 2025 08:31:31 FOUS30 KWBC 270831 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 431 AM EDT Sat Sep 27 2025 Day 1 Valid 12Z Sat Sep 27 2025 - 12Z Sun Sep 28 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHWEST AND MID-ATLANTIC... Southwest/Southern Rockies/High Plains A closed upper low over the Southwest will generate scattered=20 thunderstorm activity across the region and into parts of the=20 Southern High Plains/Rockies beginning this afternoon. Anomalous=20 moisture (1in+ PWAT/2-3 StD) within a bouyant environment 1000+=20 MUCAPE should yield modest rain rates of over an inch/hr,=20 especially over favorable upslope terrain. Burn Scars and slot=20 canyons will be among the most susceptible to flash flooding. Mid-Atlantic/Southeast An upper trough will continue supplying ample moisture (1.5-2in+=20 PWAT) and sufficient instability (500 J/Kg+) to the Mid- Atlantic/Southeast Coastline today. Storms should develop within the warm sector of a stationary front draped across the Southern Appalachians and Mid-Atlantic Coast. The heaviest rainfall (1-2 in/hr rates) should focus around the aforementioned front where=20 favorable right entrance region dynamics will likely develop and=20 prolong storms during peak heating hours. Kebede Day 2 Valid 12Z Sun Sep 28 2025 - 12Z Mon Sep 29 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF FAR WEST TEXAS, NEW MEXICO AND SOUTHWESTERN COLORADO... Southwest/Four Corners/Southern High Plains/Rockies The upper low in the Southwest is expected to open as it lifts=20 into the Rockies on Sunday. The threat for excessive rainfall thus=20 expands a bit around the trough as the fetch of moisture from the=20 previous day rotates around the low and into parts of the Great=20 Basin and Four Corners. Some elevated instability 500 J/Kg+ MUCAPE=20 could generate 0.5-1.5 in/hr rates, especially over parts of New=20 Mexico, where a slight risk is in effect. Antecedent rainfall from=20 Saturday should lower FFGs, making soils more vulnerable to flash=20 flooding. Slot canyons, dry washes and upslope areas will likely be the most susceptible to runoff. Southeast Guidance continues to trend farther away from the Southeast Coast with the axis of substantial QPF associated with a tropical=20 cyclone moving through the Bahamas at the beginning of the day 2=20 period (Sunday morning). Given the uncertainty of the system's=20 track, it's difficult to say with any confidence if/where the most=20 impactful rainfall will occur, thus a broad marginal is in place=20 from the Outer Banks down to Miami for now. Kebede Day 3 Valid 12Z Mon Sep 29 2025 - 12Z Tue Sep 30 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST AND MID-ATLANTIC... Southeast/Mid-Atlantic Tropical moisture arrives along the Southeast/Mid-Atlantic Coast=20 on Monday ahead of the associated cyclone, which is currently=20 forecast to be east of Georgia by Tuesday morning. Current=20 deterministic guidance has between 2-4 inches of rainfall occurring along the Carolina Coast with isolated higher amounts. Models are=20 trending away from the coast with the cyclone's track, which is=20 reflected in a decreasing QPF trend with this cycle as well. Northern California/Southwest Oregon A deep East Pacific trough will bring broad diffluent flow aloft=20 over the Northwest Coast beginning Monday morning. Scattered=20 showers and thunderstorms may develop along the leading edge of a=20 surface front, where the presence of weak instability (350 J/Kg MUCAPE) and modest moisture (~1 in. PWAT) could produce localized=20 flash flooding along the northern California/southwest Oregon Coasts and inland into the Southern Cascades and northern Sierra. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9AScklAg2iERZHfLXW1ILyO2KW8JRkmC_4fDKOUUKDXR= 5EhVqu0on3ilRiGJ0dnOyGTY9MrIvhovEj_B2RuxeedEUFM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9AScklAg2iERZHfLXW1ILyO2KW8JRkmC_4fDKOUUKDXR= 5EhVqu0on3ilRiGJ0dnOyGTY9MrIvhovEj_B2RuxGOP8I0w$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9AScklAg2iERZHfLXW1ILyO2KW8JRkmC_4fDKOUUKDXR= 5EhVqu0on3ilRiGJ0dnOyGTY9MrIvhovEj_B2RuxwewnExA$=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) .