Quantitative Precipitation Forecast
Issued by NWS
Issued by NWS
608 FOUS30 KWBC 112031 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 331 PM EST Tue Nov 11 2025 Day 1 Valid 16Z Tue Nov 11 2025 - 12Z Wed Nov 12 2025 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Wegman/Kleebauer Day 2 Valid 12Z Wed Nov 12 2025 - 12Z Thu Nov 13 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHWESTERN CALIFORNIA AND FAR SOUTHWESTERN OREGON... ...2030z Update... No significant changes for the afternoon update, other than to trim eastern portions of the inherited Marginal Risk area as the 12z CAM suite and global models are in good agreement in suggesting a later arrival (and perhaps slightly slower progression of the system). Latest QPF forecast calls for localized 1.5-3.0" totals, and the vast majority of this precipitation is expected late in the period (06-12z Thu). While the HREF suite is only just beginning to extend to this crucial later portion of the forecast, early indications suggest that medium to high (30-80%) chances for localized 0.25"/hr exceedance and low (5-10%) chances for localized 0.50"/hr exceedance (per 10-100 km neighborhood EAS probabilities). Churchill ...Previous Discussion... A deep digging positively tilted upper level trough will approach the West Coast on Wednesday night. As it approaches the coast, a strong shortwave rounding the base of the trough will initiate cyclogenesis off the California coast. The strengthening low will track north along the coast. The low`s trailing cold front will be the impetus forcing plentiful Pacific moisture (2-2.5 sigma above normal) northeastward along a corridor drawn by a 100 kt jet into the northern California and southwestern Oregon coast Wednesday evening. 850 mb flow out of the SSW will upslope along the coastal ranges on the order of 50-70 kt. MUCAPE values will remain under 100 J/kg, so any convection will likely be tied to locally increased lift along the mountains associated with the upslope, resulting in a period of heavy rain. Soil moisture levels in this area are around normal for this time of year, which should support much of the rainfall in the area being beneficial. However, given potential for a bit of elevated instability as well as the upslope, there remains some possibility for isolated instances of flash flooding, especially between the coastal ranges and the coast. The inherited Marginal Risk was left unchanged. Some uncertainty remains as to the timing of the heavy rainfall, namely how far east the rain can get before the 12Z Thursday start of the day 3 period. The latest guidance has been slower, so the Marginal Risk may be able to be pulled from the western foothills of the Sierras with future updates should those trends continue. Wegman Day 3 Valid 12Z Thu Nov 13 2025 - 12Z Fri Nov 14 2025 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF NORTHERN, CENTRAL, AND SOUTHWESTERN CALIFORNIA... ...2030z Update... While the forecast reasoning below remains largely unchanged, the inherited Marginal Risk was expanded significantly to account for still rather large spread/uncertainty with regard to the speed of progression of the system Thursday morning into late Thursday night. While the current forecast calls for localized 1.5-3.0" rainfall totals, several deterministic solutions (12z GFS, UKMET, CMC, and the experimental RRFS) suggest the potential for localized 3" exceedance (with the CMC and CMCreg in particular suggesting impressive localized 4"+ totals). In addition, the latest ensemble guidance is also supportive of localized 3" exceedance (ECENS and GEFS exceedance probabilities of 5-10%, which will certainly increase once in CAM range and expressed as neighborhood probabilities). As of the 12z cycle, the ECENS is a bit slower (indicating lingering heavy rainfall as far back/north as far southwestern OR) with the GEFS and other solutions a bit quicker. While there is not enough confidence to introduce any Slight Risk areas with this update, it remains a distinct possibility with subsequent updates. Churchill ...Previous Discussion... The inherited Marginal Risk was left mostly unchanged across California with this update. A small expansion up the western foothills of the Sierras was added given the flashy nature of some of the smaller streams and creeks to a period of heavy rain. The cold front that will barrel into the coast Wednesday evening will continue eastward into Thursday through the Sacramento Valley. The front will push southward down the coast with time as well, with heavy rain beginning in L.A. Thursday afternoon and evening. Within the Marginal Risk area, the greatest threat for flash flooding will be on previous burn scars in southern California`s Transverse Ranges, as well as in any urban areas at the foot of those mountains. Upslope flow from an increasingly parallel front will cause heavy mountain snow amounting to a few feet in spots, but at the lower elevations, heavy rain may cause localized flash flooding. Fortunately, the cold front causing the heavy rain will remain progressive through this period. This will limit the time any heavy rain will impact any one area of California. Meanwhile, the forcing for heavy rain will weaken as the front pushes south, which should somewhat offset (due to diminishing rain rates) any flash flooding potential, which would otherwise be increased due to urbanization and burn scars in and along steep terrain. The Marginal Risk may need to be expanded further north up the Sacramento Valley into portions of northern California with future updates if guidance trends of slowing the speed of the front continue. Due to the aforementioned weakening of the front, a Slight Risk was not considered with this update, but could be possible in the most sensitive areas, especially if forecast rainfall amounts increase further with future updates. Should a Slight Risk be needed, it appears most likely in the Transverse Ranges northwest of Los Angeles. Wegman Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt