286  
AWUS01 KWNH 212235  
FFGMPD  
AZZ000-220234-  
 
MESOSCALE PRECIPITATION DISCUSSION 0993  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
635 PM EDT SUN OCT 21 2018  
 
AREAS AFFECTED...SOUTHERN ARIZONA  
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE  
 
VALID 212234Z - 220234Z  
 
SUMMARY...THUNDERSTORMS CAPABLE OF PRODUCING HOURLY TOTALS OF 1-2"  
WILL BE POSSIBLE ACROSS FAR SOUTHERN ARIZONA THROUGH LATE  
AFTERNOON AND EARLY EVENING.  
 
DISCUSSION...IN DIVERGENT FLOW ALOFT WITH AN OPEN WAVE ACROSS  
SOUTHERN CALIFORNIA, COMBINED WITH PEAK HEATING WHERE INSTABILITY  
IS AROUND 1500-2000 J/KG, THUNDERSTORMS HAVE DEVELOPED ACROSS  
SOUTHERN ARIZONA. RECENT ANALYSIS SHOWS A TONGUE OF HIGHER PWATS  
(1-1.1") ACROSS THE AREA, WHICH IS IN THE 90TH PERCENTILE AND  
ROUGHLY 1-2 SD ABOVE NORMAL. CONVECTION HAS BEEN DRIFTING  
NORTHEASTWARD PER LATEST KEMX RETURNS, WHERE HOURLY RATES HAVE  
EXCEEDED 1-2".  
 
HI-RES MODELS HAVE NOT HANDLED THIS ACTIVITY WELL, BUT WOULD  
EXPECT A SLOW PROGRESSION NORTHEAST FOR THE NEXT FEW HOURS UNTIL  
PEAK HEATING/INSTABILITY WANES. ADDITIONAL TOTALS OF 1-2", WITH  
LOCALLY HIGHER AMOUNTS, WILL BE POSSIBLE OVER AREAS WITH LOWER FFG  
(1-HR 1" OR LESS) WHICH MAY LEAD TO LOCALIZED FLASH FLOODING.  
 
TAYLOR  
   
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...PSR...TWC...  
 
ATTN...RFC...CBRFC...  
 
LAT...LON 33470983 32030947 30711000 30381073 31521201  
33041100  
 
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