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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