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   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   1100 AM EST Fri Nov 14 2025   
      
   Day 1   
   Valid 16Z Fri Nov 14 2025 - 12Z Sat Nov 15 2025   
      
   ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   SOUTHERN CALIFORNIA...   
      
   ...16Z update...   
      
   ...Southern California...   
      
   No significant changes to the forecast were needed with a Moderate   
   Risk maintained across southern California. 12Z sounding data from   
   NKX showed a PW of 1.36 inches (likely a daily max) with an=20   
   ongoing (15Z) moisture surge into eastern Santa Barbara, Ventura=20   
   and Los Angeles counties. The early morning (15Z) IVT values along=20   
   the coast were near 500 kg/m/s and these values are expected to=20   
   weaken during the day today with some lowering of PW values and 850   
   mb wind speeds. A lingering flash flood threat will continue for=20   
   at least the beginning of the ERO period until later this evening=20   
   followed by a relative lull toward 00Z. Tonight however, low level=20   
   winds will veer toward the south and south-southeast as the=20   
   vorticity max mentioned in the previous discussion approaches,=20   
   along with a secondary surge in IVT values back toward 500 kg/m/s=20   
   and weak instability, supporting the potential for peak hourly=20   
   rainfall near 1 inch into the favored terrain.=20   
      
   The focus of heavy rain over the next 24 hours looks to be from   
   eastern Santa Barbara into Ventura counties, but potential for 2-4   
   inches (locally higher) will exist throughout the Transverse Ranges   
   through 12Z Saturday. This threat will continue into the Day 2 ERO   
   period where a Moderate Risk continues from the existing Day 1   
   outlook.   
      
   ...Washington State...   
      
   No changes were needed for this update with potential for an   
   additional 1 to 3 inches for the Olympics and Cascades through 12Z   
   Saturday. The lower end of that 1-3 inch range is anticipated for   
   the Olympics with maxima of 3 to perhaps 4 inches in the Cascades=20   
   with rates likely staying below 0.5 in/hr. However, wet antecedent=20   
   conditions will continue to warrant a Marginal Risk for the region.   
      
   Otto   
      
   ...previous discussion follows...   
      
      
   A deep positively tilted trough off the central California coast   
   early this morning will cut off entirely from the main jet stream   
   by this afternoon. A maximum of shortwave upper level energy will   
   rotate around the southern periphery of the cutoff low, which will   
   shift it from positive to negative tilt. All the while the cutoff   
   low will bodily drift east towards the southern California coast.   
   The result of this pattern will be a plume of moisture tracking NNE   
   into the southern California coast, roughly orthogonal to the   
   western Transverse Ranges. The heaviest rains in the Transverse   
   Ranges are near Point Conception. They will shift eastward with   
   time along the coast towards the L.A. Basin by this afternoon. The   
   plume as a whole will weaken with time through the evening hours   
   due to the aforementioned realignment of the cutoff low and   
   associated upper level energy. However, on Friday night, as the low   
   becomes negatively tilted and that upper level shortwave approaches   
   the coast, rainfall rates will rapidly increase. There has been   
   some uncertainty as to where the plume of heaviest rain Friday   
   night will set up, but the latest suite of guidance suggests that   
   plume will be right over L.A. and points immediately west,   
   including the hard hit areas from last year's wildfires around   
   Malibu and the Palisades.   
      
   In coordination with LOX/Oxnard, CA forecast office, a Moderate   
   Risk upgrade was introduced with this update. This upgrade is   
   largely for the heavy rain expected through the overnight Friday   
   night as the approaching shortwave not only increases rainfall   
   rates, but also it advects some instability into the coast, which   
   in turn will support elevated thunderstorm activity. Rainfall rates   
   within the storms may approach 1 inch per hour, especially as those   
   storms move over the most favored upslope areas on the L.A. facing   
   side of the Transverse Ranges. Timing will be everything as to how   
   widespread the impacts will be. However, given the plume's near   
   worst- case- scenario position from Malibu and the highly   
   urbanized L.A. Basin, and the unusual amounts of both moisture   
   available and instability for November, it's very possible that the   
   heavy rain over burn scars and urbanized areas could quickly worsen   
   resultant flash flooding leading to Moderate level impacts late   
   Friday night. Further, since the heaviest/worst of the storm will   
   continue into Day 2/Saturday, the Moderate Risk serves as a likely   
   "storm total" threat level that both improves continuity in the   
   forecast, but also encourages preparation during any dry or lighter   
   rain periods in the L.A. area today.   
      
   The rain will continue north into the southern San Joaquin Valley   
   today, and continuing into the southern Sierras a portions of   
   southwest Nevada as well. While the rates and total rainfall in   
   these areas to the lee of the Transverse Ranges will be lighter,   
   their drier climate will make them similarly susceptible to flash   
   flooding due to the lower water thresholds needed to support flash   
   flooding. Given recent drier weather and the worst of the storm   
   forecast to arrive on Saturday, the area remains in a Marginal Risk   
   for this update.   
      
   ...Washington State...   
      
   A Marginal Risk across portions of western Washington State was   
   unchanged with this update as a stalled out cold front becomes a   
   warm front through the period, resulting in a longer duration   
   mostly light rainfall across the area, with the favored   
   upslope/west facing slopes of the Olympics and northern Cascades   
   most likely to see isolated instances of flash flooding.   
      
   Wegman   
      
   Day 2   
   Valid 12Z Sat Nov 15 2025 - 12Z Sun Nov 16 2025   
      
   ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   SOUTHERN CALIFORNIA...   
      
   The peak of the heavy rainfall event across southern California   
   will occur on Day 2/Saturday. The upper level low off the coast   
   will barrel inland, drawn eastward by the strong shortwave trough   
   leading it. PWATs are expected to increase to around 1.25 inches,   
   which is as much as 4 sigma above normal for this time of year.   
   Meanwhile MUCAPE values could increase to around 250 J/kg near the   
   coast. As the low moves into central California to near the NV/CA   
   border in central CA/southwest NV, the plume of heaviest rain will   
   push inland and slowly weaken with time. Meanwhile, an additional   
   shortwave will round the low and impact much of southern California   
   into Saturday night.   
      
   Given the expected very wet Friday across much of southern   
   California, and with the heaviest rains expected to be ongoing at   
   the start of the period, a Moderate Risk upgrade was also   
   introduced on Day 2/Saturday. This is in line and for many of the   
   same areas as on Day 1/Friday. However, unlike Friday's rains,   
   these rains will have Friday's rains to build upon, worsening the   
   number, severity, and duration of the heaviest rains across   
   southern California. Thus, certainty with the Moderate Risk on   
   Saturday is much higher than on Friday.   
      
   As on Friday, as the shortwave and in this case the entire upper   
   low push ashore, expect occasionally heavy rain with embedded   
   thunderstorms to continue north and east to impact the southern   
   Sierras of central California, much of southern Nevada, including   
   Las Vegas, and much of western Arizona. Rainfall rates will remain   
   high as heavy rains impact much of these areas. Thus, in   
   coordination with VEF/Las Vegas, NV forecast office, the inherited   
   Slight Risk was expanded east to include Esmeralda, southern Nye,   
   and Clark counties in southwestern Nevada, as well as Mohave County   
   in Arizona. Urban concerns will be present across the Las Vegas   
   metro area from the heavy rains as well. The desert soils in this   
   area should be rather hydrophobic from recent dry weather, which   
   should support increased runoff, especially early in the day.   
      
   In coordination with LOX/Oxnard, CA and HNX/Hanford, CA forecast   
   offices, a Moderate Risk area was introduced from Point Conception   
   east through L.A. This especially includes the Palisades fire burn   
   scar near Malibu, as well as others in the area. Debris flows and   
   fast moving water are likely as the rainfall drains into the flashy   
   creeks and streams that drain the Transverse Ranges. Expect the   
   heaviest rains to impact the L.A. Basin through Saturday morning,   
   with diminishing rates down to occasional showers and light rain   
   from Saturday afternoon through the overnight.   
      
   Wegman   
      
   Day 3   
   Valid 12Z Sun Nov 16 2025 - 12Z Mon Nov 17 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF   
   CENTRAL AND NORTHERN CALIFORNIA...   
      
   As the cutoff low that impacted southern California on Friday and   
   Saturday moves inland, it will rapidly weaken and quickly become a   
   non-factor as far as heavy rain is concerned. Nonetheless,   
   especially early Sunday morning, light rainfall associated   
   therewith may be ongoing. The bigger event will be a cutoff low   
   that follows a similar pattern to the first, but much further north   
   and with less of a tropical connection than the first. The cutoff   
   low will sag southward from Oregon into northern California. Upper   
   level energy associated therewith will use what moisture it can   
   muster to support a progressive cold front that will sweep west to   
   east across the state. Once again there could be some modest   
   elevated instability of 300 J/kg or less with the front. Thus,   
   expect some convection/thunderstorms to be associated with the   
   front. Those periods of heavy rain when combined with recent heavy   
   rains from today could lead to isolated instances of flash flooding   
   in prone areas. Thus, a Marginal Risk was introduced with this   
   update for much of central and northern California, as well as far   
   southwestern Oregon.   
      
   Wegman   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!7twNVuyK1rphaQuEVUwNLAsJOFX3cXaOyba8CdT9o9dy=   
   c8uuCxBuCswHRqajJGG0MMoQ47GNpOI7fqXl4lVX4hH8gTY$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!7twNVuyK1rphaQuEVUwNLAsJOFX3cXaOyba8CdT9o9dy=   
   c8uuCxBuCswHRqajJGG0MMoQ47GNpOI7fqXl4lVXBuDLS8o$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!7twNVuyK1rphaQuEVUwNLAsJOFX3cXaOyba8CdT9o9dy=   
   c8uuCxBuCswHRqajJGG0MMoQ47GNpOI7fqXl4lVX6sDKDdU$=20   
      
   =3D =3D =3D   
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