MESOSCALE PRECIPITATION DISCUSSION 0271
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
612 PM EDT WED MAY 24 2017

AREAS AFFECTED...EASTERN WV...WESTERN VA...NORTHWEST NC

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 242215Z - 250415Z

SUMMARY...CONVECTION TRACKING OVER AREAS WITH LOWER FLASH FLOOD
GUIDANCE VALUES COULD RESULT IN A FLASH FLOOD THREAT THROUGH THE
LATE EVENING HOURS.

DISCUSSION...LINES OF LOW TOPPED CONVECTION CONTINUE TRACKING FROM
SOUTH TO NORTH ACROSS CENTRAL AND WESTERN NC INTO FAR SOUTHWEST VA
AND EASTERN WV. THE CONVECTION BECOMES ELEVATED AS IT MOVES NORTH
OF A WARM FRONT OVER WESTERN NC...AS THE BEST INSTABILITY BECOMES
CUT OFF FROM THE SOUTH.

A 20 TO 25 KNOT LOW LEVEL FLOW SOUTHEAST FLOW AT 850 MB CONTINUES
TO SUPPLY 1.25 TO 1.50 INCH PRECIPITABLE WATER AIR TO THE ELEVATED
CONVECTION OVER SOUTHWEST VA... WHERE LOCAL RADARS SHOWED HOURLY
RAINFALL RATES GENERALLY AN INCH OR LESS.

AS SHORT WAVE ENERGY IS EJECTED FROM A CLOSED MID LEVEL LOW OVER
SOUTHERN IN AND NORTHERN KY...DIVERGENCE ALOFT INCREASES OVER THE
MID ATLANTIC STATES...RESULTING IN AN ENLARGING AREA OF SYNOPTIC
SCALE ASCENT. THE COMBINATION OF LOW LEVEL UPSLOPE INFLOW..A
DEEPENING MOISTURE PLUME...AS WELL AS INCREASING SYNOPTIC SCALE
LIFT SHOULD RESULT IN COVERAGE OF SHOWERS AND ELEVATED
THUNDERSTORMS OVER FAR NORTHWEST NC...MUCH OF WESTERN VA...AND FAR
EASTERN WV THROUGH THE EVENING HOURS.

THE BEST LIFT IS EXPECTED TO PASS OVER THIS AREA DURING THE
EVENING HOURS (GENERALLY BETWEEN 23Z AND 03Z)...DURING WHICH TIME
RAINFALL RATES ARE EXPECTED TO STEADILY INCREASE. HOWEVER...IT IS
UNCLEAR HOW MUCH OF A CONVECTIVE ELEMENT IS PRESENT DURING THE
BEST SYNOPTIC SCALE ASCENT. THE LATEST RAP SHOWED DECREASING
VALUES OF MUCAPE (DROPPING BELOW 250 J/KG BY 03Z)...WHICH WOULD
SUGGEST THAT MUCH OF THE MODERATE TO HEAVY RAIN THAT FALLS WILL
NOT HAVE ANY CONVECTIVE ENHANCEMENTS TO THE RAINFALL RATES.

THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE AS LOW AS 1.00 TO 1.50
INCHES ACROSS MUCH OF EASTERN WV AND SOUTHWEST VA. MUCH OF THE
HIGH RESOLUTION GUIDANCE VALUES NEAR THESE VALUES...BUT WITHOUT
THE CONVECTIVE RAINFALL RATES...TRUE FLASH FLOODING WILL BE
DIFFICULT.

HAYES

ATTN...WFO...AKQ...LWX...MRX...RAH...RLX...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...

LAT...LON   38927944 38427816 38157806 36857815 35567909
            35567938 35547975 36118017 36418032 36198099
            36178131 36238153 36498168 37038167 37438153
            37758139 38118113 38578062