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   CAZ000-242049-   
      
   Mesoscale Precipitation Discussion 1270   
   NWS Weather Prediction Center College Park MD   
   351 AM EST Wed Dec 24 2025   
      
   Areas affected...portions of southern California   
      
   Concerning...Heavy rainfall...Flash flooding likely   
      
   Valid 240849Z - 242049Z   
      
   Summary...Heavy rainfall was beginning to develop across western   
   portions of the Transverse Ranges.  The rain will expand in   
   coverage through 20Z/noon Pacific Time.  Widespread 3-5 inch   
   totals are expected, with isolated 8-inch amounts possible.  A   
   dangerous scenario is unfolding, with widespread and significant   
   impacts from flash flooding and debris flows expected.   
      
   Discussion...The onset of a landfalling atmospheric river was   
   beginning to increase rain rates across the western Transverse   
   Ranges over the past hour or so (per radar mosaic/MRMS).  The   
   rainfall was associated with an axis of very strong   
   south-southwesterly low-level flow (50+ knots at 850mb) beginning   
   to make eastward progress into the discussion area.  This flow was   
   oriented perpendicularly to the Transverse Ranges, promoting   
   strong orographic lift/ascent of an abundantly moist airmass (PW   
   values from 1-1.5 inch per SPC Mesonanalyses). Weak surface-based   
   instability was evident near immediate coastal areas as well.  The   
   regime was already beginning to spread 0.5-0.8 inch/hr rain rates   
   into Santa Barbara County over the past hour.   
      
   The overall pattern will shift only slowly eastward across the   
   discussion area as a strong low pressure area west of Eureka, CA   
   migrates northeastward/inland toward the Pacific Northwest.  Heavy   
   rainfall will increase in coverage and intensity through the next   
   6-12 hours as well.  A few areas of 1 inch/hr rain rates can be   
   expected, and 3-5 inch totals (with local amounts reaching 8   
   inches) can be expected across the Transverse Ranges through   
   20Z/noon Pacific time.  This rain will fall on sensitive terrain   
   (i.e., burn scars, low-lying areas) creating a potentially   
   dangerous scenario for widespread rapid runoff, flash flooding,   
   debris flows, and rock/land slides.  Significant impacts are   
   expected in this regime.   
      
   Other areas displaced from the Transverse Ranges could experience   
   heavy rain as well (1-3 inch amounts).  Flash flooding could occur   
   - especially in urban areas and over burn scars.   
      
   Cook   
      
   ...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=   
   DZ3fjg!5v6fNz6JRQ5fk-0hyZxoJYFxEGoCCYMVkWJrrpQsthUeto2mTJiSOx38Ww8po5CA8mfd=   
   Gm2Qv9XSl3e2HhlGEHt32pQ$  for graphic product...   
      
   ATTN...WFO...HNX...LOX...MTR...SGX...   
      
   ATTN...RFC...RSA...NWC...   
      
   LAT...LON   37651974 37051892 36301813 35571804 35061803=20   
               34731784 34541734 34251686 34061670 33921714=20   
               33301749 33911887 34442054 35222101 35852150=20   
               36312170 36322135 35922080 35371996 35431941=20   
               36031933 36931957 37371990=20   
      
   =3D =3D =3D   
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   --- SBBSecho 3.28-Linux   
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