Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Nov 02 2025 19:53:59 FOUS30 KWBC 021953 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 253 PM EST Sun Nov 2 2025 Day 1 Valid 16Z Sun Nov 02 2025 - 12Z Mon Nov 03 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Several model solutions are fairly aggressive in depicting heavy rainfall along coastal areas of North Carolina tonight into early tomorrow (Monday). Cooling aloft (from eastward movement of a deep mid/upper trough currently over Middle Tennessee) and warming/moistening (from advection over the Gulf Stream) may result in enough surface-based instability for deep convection along coastal areas and the Outer Banks. Concerns about the magnitude of instability and sensitivity of ground conditions (with marshy ground areas and only modest streamflow signals via USGS Water Dashboard) lend considerable doubt regarding inland flash flood potential. A small Marginal area might be needed in later and/or special outlook updates if inland convective signals become more pronounced later this evening. Cook/Churchill Day 2 Valid 12Z Mon Nov 03 2025 - 12Z Tue Nov 04 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Orrison Day 3 Valid 12Z Tue Nov 04 2025 - 12Z Wed Nov 05 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHWESTERN CALIFORNIA AND FAR SOUTHWESTERN OREGON... 2030Z Update... The latest multi-model consensus continues to advertise arrival of strong atmospheric river activity late Tuesday and into early Wednesday morning across portions of especially southwest OR and northwest CA. This will be driving by strong jet energy rounding the base of a deep layer trough amplifying offshore of the West Coast. Enhanced deep layer Pacific moisture transport and orographic ascent along the coastal ranges will yield heavy rainfall. Generally 2 to 4 inch rainfall totals are still anticipated by early Wednesday morning across the southwest-facing slopes of far southwest OR and northwest CA, but some spotty 5+ inch totals will be possible given the level of elevated IVT magnitudes which may peak Tuesday night around 1000 kg/ms. Given=20 the consistent meteorological setup compared to continuity, only=20 very minor tweaks were made to the Marginal Risk for excessive=20 rainfall for this update. Orrison Previous discussion... The next strong landfalling atmospheric river (IVT > 750 kg/ms)=20 looks to impact coastal portions of northern CA/far southwestern OR come Tuesday afternoon, likely peaking in strength in the evening=20 to overnight period. Initial low-level flow earlier in the day=20 looks more ideally directed perpendicular to the coast/mountains,=20 but by the time higher IVT sets in veering to the SW-SSW may=20 mitigate the effectiveness of the topographic lift (with otherwise=20 limited instability as MUCAPE of less than 250 J/kg is forecast).=20 Even still, this is a relatively warm system (with the cold core=20 staying offshore until beyond Day 3) and PWATs of 1.2-1.4" are in=20 the vicinity of the 90th percentile climatologically. Rainfall=20 totals of 2-4" are generally expected (and may locally exceed 4"),=20 and much of that could occur in a 6-12 hour period. The inherited=20 Marginal Risk is sufficient (in-line with the latest GEFS-driven=20 machine learning first guess field) and has been maintained (with=20 only minor adjustments based on the latest models QPF footprint).=20 Any flash flood impacts are most likely where relatively high=20 rainfall rates (0.25"+/hr) coincide with sensitive burn scars. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_-it8BWFnl6dQ6tCbTm_241cAqo4S5cRwbrW8oRxXyKI= AyvcBO01HdDpQAEhu7B1ufccfLFFgfPsFZlIHGYqNOkRLis$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_-it8BWFnl6dQ6tCbTm_241cAqo4S5cRwbrW8oRxXyKI= AyvcBO01HdDpQAEhu7B1ufccfLFFgfPsFZlIHGYqDAUKp3Y$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_-it8BWFnl6dQ6tCbTm_241cAqo4S5cRwbrW8oRxXyKI= AyvcBO01HdDpQAEhu7B1ufccfLFFgfPsFZlIHGYqrOhKfFE$=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) .