Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 28 2025 08:29:48 FOUS30 KWBC 280829 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Sun Sep 28 2025 Day 1 Valid 01Z Sun Sep 28 2025 - 12Z Sun Sep 28 2025 ....THERE'S A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF NEW MEXICO AND PORTIONS OF FAR WESTERN TEXAS/SOUTHERN COLORADO... ....Four Corners/Southwest... An upper trough centered over the Southwest will continue=20 directing mid-level vortices northward through the Four Corners=20 region today. Moisture from Tropical Cyclone Narda in the East=20 Pacific will continue surging north into the Four Corners, where=20 scattered showers and thunderstorms are likely to proliferate throughout the day. PWATs between 1-1.5 inches within the right entrance=20 region of the upper jet and modest instability around 500-1000+=20 J/Kg (MLCAPE) could yield rain rates between 0.5-1 in./hr.,=20 especially where the slight risk is currently drawn. Burn scars,=20 scars slot canyons and upslope areas within the risk areas are=20 especially vulnerable to flash flooding.=20 HREF's neighborhood exceedance probabilities of 2 in. in 24 hours=20 are between 25-50% while EAS probabilities of exceeding 0.5 in.=20 hover around 20-40% within the depicted slight risk area. ....Southeast... An upper trough will pivot eastward over the Southeast while=20 moisture from T.C. Nine continues surging northward toward the=20 Southeast Coast. Current guidance keeps the axis of heaviest QPF=20 offshore, but enough moisture may propagate far enough north and=20 west to interact with a surface front draped along the coast and=20 produce localized excessive rainfall. HREF EAS exceedance=20 probabilities of 1 inch in 24 hours are between 5-15% along much=20 of the Carolina Coast today, which supports the marginal risk area depicted. Kebede Day 2 Valid 12Z Sun Sep 28 2025 - 12Z Mon Sep 29 2025 ....THERE'S A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CAROLINA COAST... ....Southeast... Guidance continue to depict T.C. Nine propagating north toward the Southeast Coast on Monday, while a surface front draped along the=20 coast acts as the focus for heavy rainfall. QPF has trended=20 downward given slowing trends in the track of T.C. Nine on Monday. The GFS suite in particular diverges most from the Canadian and=20 Euro suites when depicting the system's slower forward motion.=20 Despite this, enough moisture should work its way into the coast and interact with the surface front to generate scattered thunderstorms. There'll be enough moisture (1.5-2.5in PWATs) and instability=20 (1000+ J/KG MUCAPE) present to support rainfall rates in excess of 1 in./hr.. ....Northern California/Great Basin/Southern Cascades... An upper low centered over the East Pacific will send mid-level=20 vortices into the West Coast on Monday. Pacific moisture may=20 collide with the remnant tropical moisture from Narda to produce=20 heavy rainfall from northern California into the Great Basin.=20 Synoptic forcing provided by a strong surface cold front should=20 focus PWATs in the range of 0.75-1.25 in. to produce quarter inch=20 rain rates along the immediate coast. More robust instability over=20 the Great Basin should yield higher rain rates between 0.5-1=20 in./hr. in some areas. Upslope enhancement may generate higher=20 totals in parts of the terrain. Kebede Day 3 Valid 12Z Mon Sep 29 2025 - 12Z Tue Sep 30 2025 ....THERE'S A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE CAROLINA COAST... ....Southeast... The inherited marginal and slight risk areas along the Southeast=20 Coast were downsized based on trends in the guidance suggesting=20 T.C. Nine's hard turn out to sea on Tuesday. Despite the resulting smaller QPF footprint than previous cycles, the flash flood risk=20 remains. Instability will be negligible (less than 500 J/Kg=20 MUCAPE), which supports the possibility that the flood threat will be due to runoff over saturated soils from Sunday and Monday's=20 rainfall. Exceedance probabilities of over 2 inches is over 10% in the 00z ECENS/CMCE, while below 10% in the GEFS along the=20 immediate Carolina Coast. Kebede Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9CYiVEneZMixDw3UL5rD9-gc3wknJ8S7ajYNrYVy8laI= -OdCwgYjk8PgU-OpCcCOUI1bgfGEhDQ4uNQSes0gJ8-bKFE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9CYiVEneZMixDw3UL5rD9-gc3wknJ8S7ajYNrYVy8laI= -OdCwgYjk8PgU-OpCcCOUI1bgfGEhDQ4uNQSes0gDqUrKE0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9CYiVEneZMixDw3UL5rD9-gc3wknJ8S7ajYNrYVy8laI= -OdCwgYjk8PgU-OpCcCOUI1bgfGEhDQ4uNQSes0g4as4coA$=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) .