712  
AWUS01 KWNH 151402  
FFGMPD  
VAZ000-NCZ000-151800-  
 
MESOSCALE PRECIPITATION DISCUSSION 0638  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1001 AM EDT SAT AUG 15 2020  
 
AREAS AFFECTED...CENTRAL/SOUTHERN VA  
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE  
 
VALID 151356Z - 151800Z  
 
SUMMARY...LOW AREAL COVERAGE OF VERY HEAVY RAIN EXPECTED OVER THE  
NEXT FEW HOURS OVER PORTIONS OF CENTRAL/SOUTHERN VA INTO FAR  
NORTHERN NC. 3 TO 5 INCHES OF ADDITIONAL RAINFALL MAY LEAD TO  
CONTINUED FLASH FLOODING ATOP NEARLY SATURATED SOILS.  
 
DISCUSSION...SATELLITE IMAGERY LOOPS OF THE 6.9 MICRON WATER VAPOR  
CHANNEL HELPED IDENTIFY TWO SUBTLE VORTICITY MAXIMA OVER THE  
MID-ATLANTIC REGION AT 13Z. ONE WAS LOCATED OVER SOUTH-CENTRAL VA  
(BEDFORD AND PITTSYLVANIA COUNTIES) WITH ANOTHER IN WESTERN NC  
(IREDELL AND ROWAN COUNTIES). LOCALLY HEAVY RAINFALL WITH OBSERVED  
RATES, SOMETIMES IN EXCESS OF 2 IN/HR, WERE NOTED EAST OF THE VA  
VORTICITY MAX. ONE AREA, JUST SOUTHWEST OF RIC, WAS TIED TO A WEAK  
AND SLOW MOVING MESO-LOW WITH SEVERAL REPORTS OF 3-5 INCHES OF  
RAIN OVER THE PAST 6 HOURS ENDING AT 13Z. A SECOND MESO-LOW WAS  
IDENTIFIED OVER EASTERN HALIFAX COUNTY WITH KFCX ESTIMATED  
RAINFALL RATES OVER 1 IN/HR. INSTABILITY WAS FAIRLY WEAK ACROSS  
SOUTHERN VA WITH ROUGHLY 250-750 J/KG MUCAPE IN PLACE VIA NEARBY  
12Z RAOBS AND THE SPC MESOANALYSIS PAGE, WITH HIGHER INSTABILITY  
RESIDING OVER NC.  
 
FORECASTS FROM THE RAP SHOW A SLIGHT UPTICK IN EASTERLY 850 MB  
WINDS ACROSS CENTRAL AND NORTHERN VA THROUGH 18Z, PEAKING JUST  
OVER 20 KT. MEANWHILE, TO THE IMMEDIATE SOUTH, 850 MB WINDS ARE  
FORECAST TO BE FROM THE SOUTHEAST/SOUTH WITH THE STRONGEST LOW  
LEVEL CONVERGENCE SETTING UP FROM THE PENINSULA OF EASTERN VA TO  
THE CENTRAL BLUE RIDGE MOUNTAINS JUST NORTH OF LYH. THIS LOW LEVEL  
CONVERGENCE AXIS IS EXPECTED TO HELP FOCUS MESOSCALE CLUSTERS OF  
HEAVY RAIN INTO THE EARLY AFTERNOON. SOME UPSLOPE ENHANCEMENT INTO  
THE ELEVATED TERRAIN OF WESTERN VA MAY ALSO HELP TO FOCUS HEAVY  
RAIN, BUT LACKING INSTABILITY WILL BE A MAJOR DETERRENT TO HIGHER  
RAINFALL RATES. RECENT HEAVY RAIN HAS LEFT MANY AREAS OF VA  
SATURATED, LOWERING FLASH FLOOD GUIDANCE VALUES TO 2 INCHES OR  
LESS IN MANY LOCATIONS. THEREFORE, WHILE THE COVERAGE OF HEAVY  
RAIN IS EXPECTED TO BE LOW ACROSS CENTRAL AND SOUTHERN VA INTO THE  
EARLY AFTERNOON, THE POTENTIAL FOR AN ADDITIONAL 3-5 INCHES IN ONE  
OR TWO LOCATIONS IS PRESENT, WHICH WOULD PRODUCE FLASH FLOODING  
GIVEN THE ALREADY WET GROUND CONDITIONS.  
 
OTTO  
   
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...AKQ...LWX...RAH...RNK...  
 
ATTN...RFC...MARFC...SERFC...NWC...  
 
LAT...LON 38317867 38297780 38127681 37617623 37247615  
37017593 36797565 36567572 36397593 36397643  
36357748 36547903 36757932 36987954 37367959  
37707952 38117917  
 
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