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   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   800 PM EST Sun Nov 16 2025   
      
   Day 1   
   Valid 01Z Mon Nov 17 2025 - 12Z Mon Nov 17 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SANTA LUCIA   
   RANGE OF CENTRAL CALIFORNIA...   
      
   ...16Z update...   
   Upper level flow across central-northern CA is becoming more=20   
   difluent this evening as the amplifying mid-upper level trough=20   
   pivots towards the coast. Deepening QG forcing and moistening   
   within the renewed Warm Conveyor Belt (WCB) is underway across the   
   Marginal Risk area, which was trimmed a bit for the 01Z Day 1 ERO   
   update based on the 12-18Z guidance and most recent HREF and RRFS   
   probabilistic suite. Withing the Marginal Risk area, the 18Z HREF   
   indicates pockets of 50-70% probabilities of hourly rainfall rates   
   exceeding 0.50".   
      
   Hurley   
      
      
   ...Previous discussion...   
   A pair of deep shortwaves will impact much of California through=20   
   the period today. The one that has been causing heavy rain across=20   
   much of southern California is pressing inland this morning. Rates=20   
   have come down a bit overnight due to waning instability, but much=20   
   of central California and portions of southern California remain in   
   more-or-less steady light to occasionally moderate rainfall. As=20   
   the upper low departs to the east, the steady rain across much of=20   
   inland California should diminish through this afternoon. Following   
   this first shortwave, another vigorous, deepening longwave trough=20   
   will track SSE out of the North Pacific and approach the northern=20   
   California coast late tonight/early Monday morning. This second=20   
   shortwave will have much more upper level energy with it by tonight   
   than the first does now. This longwave trough will also have some=20   
   instability with it. The result will be steady rain associated with   
   the approaching low plowing into the northern California coast=20   
   this evening, then spreading south in the form of a line of=20   
   moderate rain with embedded thunderstorms capable of brief periods=20   
   of heavy rain. It will cross the Bay area late this evening, then=20   
   push south almost to Point Conception by 12Z Mon. The heaviest rain   
   will push inland, reaching the central Sierra around the same=20   
   time.   
      
   Much of the Santa Lucia Range in central California have picked up   
   between 5 and 8 inches of rain over the last week. Continued light   
   to moderate rain may add another inch through this morning, but the   
   heavy rains tonight with the cold front will likely drop another   
   1-2 inches. Rock and landslides have been reported from today's   
   rain. Thus with shifting winds and heavy rain tonight, it's   
   probable there may be additional impacts from the storms. In   
   coordination with MTR/Monterey, CA forecast office, a Slight Risk   
   upgrade was introduced with this morning's update. Elsewhere the   
   surrounding Marginal remains unchanged.   
      
   ...Southwest Utah...   
      
   The Marginal Risk area in southwest Utah also remains unchanged.   
   Upslope flow into the Pine Valley Mountains may cause isolated   
   instances of flash flooding as the area of rain currently over   
   southern Nevada pushes east into the region, where enhanced upslope   
   will cause the rain to intensify. The highest elevations above   
   8,000 ft or so may see snow, which will limit the flooding   
   potential at lower elevations.   
      
   Wegman   
      
   Day 2   
   Valid 12Z Mon Nov 17 2025 - 12Z Tue Nov 18 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE LOS   
   ANGELES BASIN OF SOUTHERN CALIFORNIA...   
      
   ...20Z update...   
   Some modifications were made to the outlook areas in CA.   
   Specifically, extended the Slight Risk slightly westward to the   
   Central CA Coast based on the latest (12Z) CAM guidance as well as   
   HREF and RRFS 0.50"+/hr and 1.00"+/hr rainfall rate probabilities   
   on Monday. Meanwhile, also largely based on those HREF and RRFS   
   exceedance probabilities, have also hoisted a Marginal Risk across   
   southwest and central portions of AZ.   
      
   Hurley   
      
   ...Previous discussion...   
   The deep and energetic trough that will be centered off the   
   northern California coast at the start of the period will track   
   southeast down the coast to over the San Joaquin Valley by early   
   Tuesday morning. The trough will cut off into a second upper level   
   low to impact the state by Monday afternoon. The heaviest rains   
   will be out ahead of this cutoff low, where the overall flow is   
   onshore out of the southwest. A line of heavy showers with embedded   
   thunderstorms will move down the coast starting around Point   
   Conception early Monday morning, reaching the L.A. Basin around   
   midday. It will take between 2-4 hours for the heavy rain band to   
   sweep through. During that time, rainfall rates peaking between a   
   half and 3/4 inch per hour in the thunderstorms may cause widely   
   scattered instances of flash flooding, especially on the south   
   facing slopes of the Transverse Ranges down to the L.A. Basin. For   
   this reason, the inherited Slight Risk remains in place with very   
   few changes. At least some of the heavy rain will also penetrate   
   inland into some of the California Deserts, including around Death   
   Valley N.P. Given how recently the area saw heavy rains from   
   yesterday, this additional heavy rain may also cause isolated   
   instances of flash flooding. Thus, the Marginal Risk was expanded   
   north and east to include a small portion of southern Nevada.   
      
   Wegman   
      
   Day 3   
   Valid 12Z Tue Nov 18 2025 - 12Z Wed Nov 19 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   THE SOUTHWEST AND LOWER GREAT BASIN...   
      
   ...20Z update...   
   Based on the guidance trends, have expanded the Marginal Risk area   
   to include more areas off the Mogollon Rim and into the deserts in   
   southern and western AZ, southeast CA, and southeast NV. PW values   
   get near 2 standard deviations above normal in southern-western AZ   
   (0.75-1.00"), while MUCAPEs climb between 500-750 J/Kg south of   
   the Mogollon Rim and into the deserts and Phoenix Metro. This will   
   maintain the risk of elevated (0.50"+) hourly rainfall rates Tue-   
   Tue night as noted from the RRFS exceedance probabilities (through   
   00Z Wed), while also implied from the 12Z RRFS and RGEM hourly and   
   3-hourly QPFs. 24hr guidance QPFs have come up from 12Z Tue-12Z   
   Wed, especially from the global models, which is a bit concerning,   
   yet understandable considering how the upper trough begins to pivot   
   more slowly as it amplifies from the shortwave energy diving   
   southward on its backside. At this point there's still not enough   
   confidence from a duration perspective to upgrade to a Slight Risk   
   over the lower terrain (all rain) areas south of the Mogollon Rim,   
   which would include the Phoenix area, but the potential to do so   
   will exist over the next day or so.   
      
   Hurley   
      
   ...Previous discussion...   
   A Marginal Risk area across portions of Arizona and southern Utah   
   was introduced with this update. The cutoff low that will spread   
   heavy rain across the L.A. Basin on Monday will slowly push east   
   across southern California through Tuesday. Once again the heaviest   
   rains associated therewith will be out ahead/east of the low   
   center, putting Arizona and Utah in the area most likely to see   
   heavy rain. Instability will once again be non-zero, peaking   
   between 200 and 400 J/kg, which combined with above normal moisture   
   will result in an area of training thunderstorms, likely along the   
   Mogollon north and east of Phoenix. The southerly flow will   
   continue across northwest Arizona and into southern Utah, where wet   
   antecedent conditions from today's rains will support additional   
   flash flooding developing with heavy rains in the Pine Valley   
   Mountains east to Lake Powell.   
      
   Wegman   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!6bUALJcB74nu0hUfx2QLyUHHz6Sl_fUvsqe3ft5q3pWR=   
   _8SPOmKYXzgdhtDTS8kUHq02oiUxOQgG3EQ8PGUSFKc7LCI$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!6bUALJcB74nu0hUfx2QLyUHHz6Sl_fUvsqe3ft5q3pWR=   
   _8SPOmKYXzgdhtDTS8kUHq02oiUxOQgG3EQ8PGUSOWYah1s$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!6bUALJcB74nu0hUfx2QLyUHHz6Sl_fUvsqe3ft5q3pWR=   
   _8SPOmKYXzgdhtDTS8kUHq02oiUxOQgG3EQ8PGUS2XIOQJg$=20   
      
   =3D =3D =3D   
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