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   Mesoscale Precipitation Discussion 1232   
   NWS Weather Prediction Center College Park MD   
   203 PM EST Tue Nov 18 2025   
      
   Areas affected...Western Arizona, Southeast California and   
   Southern Nevada   
      
   Concerning...Heavy rainfall...Flash flooding likely   
      
   Valid 181903Z - 190103Z   
      
   SUMMARY...Flash flood risk increasing this afternoon into the   
   evening across the Colorado River basin between southeast   
   California, southern Nevada, and western Arizona. Heavy rainfall   
   potential existing through sunset leading to potential night time   
   flash flooding concerns.   
      
   DISCUSSION...Current radar/IR satellite composite indicates a   
   brief lull initiating over portions of southwest AZ and   
   southeastern CA. Meanwhile, a steady progression of a stronger   
   convective pulse over far northeast Baja will make headway to the   
   north as it migrates within the broad deep layer steering flow out   
   of the south-southwest. This is due to the proximity of the=20   
   persistent ULL presence off the southern CA coast with smaller   
   shortwave perturbations emanating around the southern and eastern   
   periphery of the upper-level circulation. Hi-res guidance,   
   especially the last several HRRR iterations have been manifesting   
   this very scenario of a brief lull, followed by the advection of   
   the next stronger mid-level perturbation exiting out of Baja and   
   shifting north along the adjacent Colorado River basin between   
   AZ/CA/NV. This will coincide within a field of relatively buoyant   
   air situated within the river basin, arcing back into southern NV   
   along the warm/cold conveyor belt transition along the northern   
   side of the surface low  analyzed over the southern tip of NV.   
      
   SBCAPE between 1000-1500 J/kg is analyzed across much of southwest   
   AZ with an extension of 500-1000 J/kg located along the northern   
   extent of the Colorado River basin between the three-state   
   intersection. This setup is poised to advect further north with a   
   greater SBCAPE alignment focused over the southern tip of NV down   
   through far-southeast CA and much of western AZ. The combination   
   of suitable vorticity advection and modest instability over an   
   area of +2 to +3 sigma PWATs will assist in a re-invigoration of   
   area convection with cells capable of 0.5-1.25"/hr at peak   
   intensity, enough to favor some  scattered flash flood prospects   
   within the confines of northern Yuma, La Paz, Mojave counties in   
   AZ, southern Clark county in NV, and far-eastern San Bernardino   
   county in CA. Some training could occur with cells materializing   
   on a north-south alignment for areas east of the Colorado River   
   given the deep layer flow remaining fairly uni-directional. This   
   could exacerbate flash flood concerns locally, leading to the   
   threat running closer to the flash flooding likely prospect,   
   especially within those western AZ counties.   
      
   Kleebauer   
      
   ...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=   
   DZ3fjg!9qZwoR-eYoOBPiD_vew7g_oNGgxGIH2VQ3sBHQQpMbB4o_gJuygnmXAcdPidULM-OuUA=   
   grZKvmqIF-vCYVPBbaCFAgc$  for graphic product...   
      
   ATTN...WFO...FGZ...PSR...VEF...   
      
   ATTN...RFC...RSA...STR...NWC...   
      
   LAT...LON   35831459 35801375 35291312 34391280 33221314=20   
               33161409 33711453 34251494 34881526 35531530=20   
   =20=20=20=20=20=20=20=20=20=20=20=20   
      
   =3D =3D =3D   
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