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   Mesoscale Precipitation Discussion 1231   
   NWS Weather Prediction Center College Park MD   
   727 AM EST Tue Nov 18 2025   
      
   Areas affected...portions of western AZ   
      
   Concerning...Heavy rainfall...Flash flooding possible   
      
   Valid 181226Z - 181826Z   
      
   Summary...An area of heavy rain with embedded thunderstorms should   
   continue across portions of western AZ over the next several   
   hours.  Hourly rain amounts to 1.5" and local 3" totals are   
   possible, which would continue isolated to widely scattered flash   
   flood concerns.   
      
   Discussion...An upper level low is sliding southeast down the CA   
   coast past Lompoc.  It has led to a broad area of divergence aloft   
   across the Southwest.  Precipitable water values of 1"+ are   
   indicated in RAP forecasts, with some GPS values across Las Vegas   
   and Phoenix in the 0.8-0.9" range.  When combined with 1000-500   
   hPa thickness values of 5550 meters, the atmosphere is saturated   
   which has led to efficient heavy rainfall across portions of   
   southwest AZ this morning, with radar indications of 1"+ in an   
   hour at times.  MU CAPE of 500-1000 J/kg exists downstream from   
   the Gulf of CA northward across southwest AZ.  Effective bulk   
   shear of 25 kts is helping to organize the convective elements.   
      
   A shortwave noted on water vapor imagery across southern CA could   
   cause some backing of the low level flow in the short term,   
   potentially shifting the heavy rain area somewhat westward with   
   time.  RAP guidance fields indicate expansion of the instability   
   pool northeast with time, which could lead to some northeast   
   shift.  When taken together, the heavy rain footprint could   
   broaden with time.  Hourly rain amounts to 1.5" and local totals   
   to 3" are possible where cells backbuild and train.  Burn scar   
   locations, arroyos/dry washes, box canyons, and urban areas should   
   be most sensitive to this rainfall.  Isolated to widely scattered   
   flash flood concerns should continue into the day today.=20   
      
   Roth   
      
   ...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=   
   DZ3fjg!7OSVbJv1SfLB2tqivOYQ7yd1rXTyeoYa0kBIta9AhWA5J57n9H8MSQQSYN4wASMHjc2P=   
   4BFi9vPa5od_YLPyG_1EGIk$  for graphic product...   
      
   ATTN...WFO...FGZ...PSR...VEF...   
      
   ATTN...RFC...STR...NWC...   
      
   LAT...LON   35721347 35591200 34471161 32961249 32731312=20   
               32951388 33841422 35121412=20   
      
   =3D =3D =3D   
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