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   Mesoscale Precipitation Discussion 1273   
   NWS Weather Prediction Center College Park MD   
   250 PM EST Wed Dec 24 2025   
      
   Areas affected...Southern and Eastern CA   
      
   Concerning...Heavy rainfall...Flash flooding likely   
      
   Valid 241950Z - 250600Z   
      
   SUMMARY...Heavy rainfall with dangerous and locally   
   life-threatening flash flooding impacts will continue to impact   
   portions of southern and eastern CA going into the evening hours   
   as strong atmospheric river activity continues.   
      
   DISCUSSION...GOES-W visible satellite imagery shows a significant   
   atmospheric river bringing heavy rain across large areas of   
   southern CA including the Los Angeles Basin, the adjacent high   
   terrain of the Transverse Range, the southern Sierra Nevada and   
   also adjacent interior desert valley locations. A deep   
   full-latitude trough offshore of the West Coast continues to shift   
   gradually eastward and is allowing for a cold front to advance   
   inland through southern CA.   
      
   This continues to help focus deep and very moist south-southwest   
   flow up out of the eastern tropical-Pacific and across the region   
   with enhanced IVT magnitudes of near 1000 kg/m/s aimed into   
   portions of Los Angeles, Orange and San Bernadino Counties. This   
   also includes the southwest facing slopes of the San Gabriel and   
   San Bernadino Mountains where enhanced orographic ascent coupled   
   with deep layer forcing and frontal convergence is yielding high   
   rainfall rates of locally over 1"/hour.   
      
   Over the next several hours, the cold front will continue to   
   settle south and east, which will allow for heavy rain to arrive   
   over the Peninsular Range of southern CA while also overspreading   
   interior areas of eastern CA including some of the desert   
   locations adjacent to the high terrain of the southern Sierra   
   Nevada.   
      
   The greatest short-term rainfall impacts and flash flooding   
   concerns will likely be over Kern, Ventura, Los Angeles, Orange,   
   and San Bernadino Counties, with eventually areas of Riverside and   
   San Diego Counties getting into heavy rainfall later this   
   afternoon and evening. Some of the rates for the aforementioned   
   southwest facing slopes of the high terrain will continue to be   
   locally near or over 1"/hour which is supported by the   
   experimental WoFS guidance which has a particular focus over the   
   next 6 hours across eastern parts of Los Angeles County, southwest   
   parts of San Bernadino County, and also Orange County.   
      
   Additional rainfall totals of 3 to 5+ inches going through late   
   this evening will be possible for the orographically favored high   
   terrain of southern CA, with as much as 1 to 3 inches elsewhere   
   including portions of eastern CA near the southern Sierra Nevada.   
   Some interior valley locations away from the terrain may even see   
   as much as 1 inch of rain.   
      
   Dangerous and locally life-threatening flash flooding is expected   
   going into the evening hours across southern CA which include   
   concerns for not only urban flash flooding, but also mud and   
   landslide activity, and debris flows near and adjacent to the more   
   sensitive burn scar locations. Areas of flash flooding will also   
   be a concern for eastern CA where heavy rains here also contribute   
   to enhanced runoff. This will include some open dry wash areas.   
      
   Orrison   
      
   ...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=   
   DZ3fjg!7iaagVot710bq-Swn8BA3WE_eOkheyqa6GwSFP3zaElDXOGKFOhl3OT5u2VyvOUtC3bb=   
   n5cnUe0YP-mJZyyxD3M1o1M$  for graphic product...   
      
   ATTN...WFO...HNX...LOX...PSR...SGX...VEF...   
      
   ATTN...RFC...RSA...NWC...   
      
   LAT...LON   37091767 36531652 35781566 35011537 34351558=20   
               33801566 33051589 32591620 32511726 33451806=20   
               33651851 34151951 34821971 35921915 36921862=20   
   =20=20=20=20=20=20=20=20=20=20=20=20   
      
   =3D =3D =3D   
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