Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Nov 05 2025 15:54:18 FOUS30 KWBC 051554 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1054 AM EST Wed Nov 5 2025 Day 1 Valid 12Z Wed Nov 05 2025 - 12Z Thu Nov 06 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. ....16z update.... Satellite trends depict the core of the moisture plume (1-1.4" TPW) continues translating eastward quickly and is currently orienting more north-south from San Francisco Bay through the Sacramento Valley. Additionally, the negative tilt base of the longer wave trough is tipping through resulting in increased directional shear which further limits the overall IVT flux, particularly orthogonally toward the Sierra Nevada Range. IVT values in the next hour or so are expected to become a more tolerable 300-500 kg/m/s.=20 Some 12z Hi-Res CAMs remain very persistent with some weak convective elements in proximity to the northern Sacramento Valley into the Trinity range, especially in Shasta county. Additional localized 2"+ with perhaps hourly rates of .5-.75" remain possible;=20 however, the areal coverage of 2"+ elsewhere along the northern=20 Sierra Nevada Range are further reducing. These factors will=20 maintain a non-zero risk of excessive rainfall with isolated=20 flooding, but the overall risk is falling below the 5% threshold=20 for maintaining a Marginal Risk.=20 This is also generally true for southwest facing Olympic Range,=20 though totals will be higher, the rates are reduced as well with=20 longer duration light to moderate rainfall totals. As such, both Marginal Risk areas have been pulled for the remainder of the Day=20 1 period (thru 06.12z). Gallina=20 ~~~Prior Discussion~~~ A strong atmospheric river impacting the PacNW will begin to wane=20 in intensity through morning, gradually ending any residual flood=20 impacts across outlooked coastal portions of CA/OR/WA.=20 Additionally, the Marginal Risk was maintained for locations=20 farther inland (upslope portions of the northern Sierras) in=20 association with the arrival of the strongest IVT from the AR.=20 Rates are still largely expected to peak near 0.5"/hr, but may=20 briefly approach as high as 1"/hr locally. Any flood impacts are=20 anticipated to be relegated to more sensitive terrain (i.e. burn=20 scars). Areal average totals are expected to range from 1-3" (with=20 much of that occurring prior to 18z), but localized 3-5" amounts=20 may occur (highest chances being in the upslope areas of Sierras=20 and the Olympics). Churchill Day 2 Valid 12Z Thu Nov 06 2025 - 12Z Fri Nov 07 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHWESTERN CALIFORNIA AND FAR SOUTHWESTERN OREGON, AS WELL AS THE OLYMPIC MOUNTAINS AND ADJACENT PORTIONS OF COASTAL NORTHWEST WASHINGTON... While the bulk of the forecast rainfall on Day 1 comes early with a distinct lull in moderate to heavy precipitation across the PacNW through much of Wednesday evening and night, precipitation looks to ramp up once again by midday Thursday (Day 2) as yet another atmospheric river makes landfall. While this AR increasingly looks to be significantly weaker and disjointed, additional rainfall totals of up to 2-3" are still possible for portions of CA/OR/WA (though forecast amounts have decreased to areal averages of 1-2"). The Marginal Risk areas were maintained for now, focused on the regions where 2-5" of rainfall may occur through the end of Day 1. There may be reconsideration of one or both of the Marginal Risk areas for futures updates, given the trend lower in the forecast rainfall amounts (while already being a relatively borderline outlook based largely on expected wet antecedent conditions). Churchill Day 3 Valid 12Z Fri Nov 07 2025 - 12Z Sat Nov 08 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9mZXauwOvXcyhyvv2UawdjNUAT2lNy8TM0SLhDyjTWnk= BhQioKYxS7qOrbxO_3jJ6Znb1hIqTRWM2YXL07Gr3gDOGpo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9mZXauwOvXcyhyvv2UawdjNUAT2lNy8TM0SLhDyjTWnk= BhQioKYxS7qOrbxO_3jJ6Znb1hIqTRWM2YXL07GrAq9xg3o$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9mZXauwOvXcyhyvv2UawdjNUAT2lNy8TM0SLhDyjTWnk= BhQioKYxS7qOrbxO_3jJ6Znb1hIqTRWM2YXL07GrfYg19PY$=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) .