Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 04 2025 19:32:06 FOUS30 KWBC 041931 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 231 PM EST Tue Nov 4 2025 Day 1 Valid 16Z 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... ....16Z update... 12Z components of the 12Z HREF kept decent continuity with the 00Z HREF regarding the strong (to locally extreme) atmospheric river forecast for the West Coast. Generally, 1-2 inches has fallen across the northern California coast over the past 24 hours with good agreement for an additional 4 to 5+ inches through 12Z Wednesday for southern Humboldt County. Localized 24 hour totals of 3+ inches are forecast for locations outside of the King Range region across the outlooked portion of northern California/southern Oregon. The greatest risk of debris flows and flash flooding across urban/low-lying locations will occur in the 06-12Z period tonight when hourly rainfall in excess of 1 inch will be possible along favored SSW facing terrain with 850-700 mb winds oriented from the S to SSW and 850 mb wind speeds possibly in excess of 80 kt along the southern Oregon coastline tonight according to the latest RAP and GFS guidance. The risk level remains Marginal due to the climatologically high flash flood guidance values across the region with the greatest risk within sensitive burn scar regions. Otto ....previous discussion follows... The next strong atmospheric river (IVT > 750 kg/ms) will begin=20 impacting coastal portions of northern CA/far southwestern OR=20 today, peaking in strength late this evening into the overnight=20 period. Forecast 24-hr totals are generally between 1.5-3.0" (but=20 may locally reach as high as 4" or so along the upslope terrain),=20 and the maintained Marginal Risk generally reflects this area.=20 While rates will generally peak between a quarter and half inch for most of the day and into the evening (with little to no impacts=20 expected), hi- res models indicate the potential for localized=20 rates of 0.5"+/hr after 06z (when IVT is peaking and oriented=20 directly inland). Much of the forecast rainfall is expected to=20 occur during the final 6-hr period, resulting in as much as=20 1.5-2.5" locally. Any flash flood impacts are still expected to=20 remain relegated to more sensitive terrain (i.e. burn scars). Churchill Day 2 Valid 12Z Wed Nov 05 2025 - 12Z Thu Nov 06 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... ....2000 UTC Update... Minimal changes were made to the Day 2 ERO, most notably to expand the Marginal Risk area over coastal areas in northwest CA to align with the Day 1 outlook. This given the overlap with the mod-heavy=20 rainfall at the end of the Day 1 period into Day 2 (i.e. Wednesday morning after 12Z). Hurley ....Previous discussion... While the aforementioned strong atmospheric river will have peaked by Wednesday morning, residual flood impacts are possible across=20 some of the same portions of northwestern CA into early Day 2. In=20 addition, some flood impacts are possible early farther inland=20 (upslope portions of the northern Sierras) with the arrival of the=20 strongest IVT (though rates peaking near 0.5"/hr will likely still=20 limit any impacts to sensitive terrain from burn scars). The=20 Marginal Risk was generally maintained with only minor tweaks. In addition, the Marginal Risk for the Olympics and vicinity in northwest WA was also maintained. Though the current forecast calls for localized 2-3" totals, some models indicate localized amounts of 3"+. Either way, this Marginal Risk is still judged to be rather borderline and driven by more long duration flood impacts (as rates may only briefly eclipse 0.5"/hr with terrain sensitivity less of an issue). Churchill Day 3 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... ....2000 UTC Update... No changes were made to the Day 3 Marginal Risk areas based on the latest guidance trends. Hurley ....Previous discussion... While the bulk of the forecast rainfall on Wednesday comes early with a distinct lull in moderate to heavy precipitation across the PacNW through much of Day 2, precipitation looks to ramp up once again by midday Thursday (Day 3) as yet another atmospheric river makes landfall. While this AR looks weaker and more disjointed overall, additional rainfall totals of up to 2-3" are forecast for portions of WA/OR/CA. A broader inherited Marginal Risk was separated into two smaller areas where models are focusing this heavier precipitation (which also coincides with areas already receiving 2-5" of rainfall between Days 1-2). While rates will likely largely be limited to 0.5"/hr, given the expected wet antecedent conditions localized flash flood impacts are possible. Churchill Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7BWavoOxtbE7GZaqwa_jwpXRLXMDuPCElMrBpTEbV2B_= 7J_E6OGkiV4YnZH5615wYYuIwhlLjCpcmKZlVROdLej-VcM$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7BWavoOxtbE7GZaqwa_jwpXRLXMDuPCElMrBpTEbV2B_= 7J_E6OGkiV4YnZH5615wYYuIwhlLjCpcmKZlVROdHmlZDnM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7BWavoOxtbE7GZaqwa_jwpXRLXMDuPCElMrBpTEbV2B_= 7J_E6OGkiV4YnZH5615wYYuIwhlLjCpcmKZlVROdgyq09K8$=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) .