MESOSCALE PRECIPITATION DISCUSSION 0167
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
631 PM EDT FRI MAY 18 2018
AREAS AFFECTED...CENTRAL VA...SE VA...NRN NC
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY
VALID 182230Z - 190430Z
SUMMARY...WARM SECTOR CONVECTION WILL CONTINUE TO FORM AND MERGE /
SLOW AS IT ENCOUNTERS A FRONTAL ZONE AND CAPE GRADIENT. ISOLATED
1.5 INCH / HOUR RATES AND 2 TO 3 INCH TOTALS POSSIBLE THROUGH
04Z...ESPECIALLY HALIFAX VA TO NEAR RICHMOND.
DISCUSSION...THE SYNOPTIC ENVIRONMENT WILL REMAIN BROADLY
SUPPORTIVE OF LIFT. VERY SLIGHT 500 MB HEIGHT FALLS ARE
ANTICIPATED OVERNIGHT. LOWER LEVEL WINDS WILL RESPOND TO BOTH THE
HEIGHT FALLS AND NIGHTFALL / DECOUPLING...BY ACCELERATING
SLIGHTLY. EXPECT THAT CONVERGENCE WILL BE MAINTAINED OR STRENGTHEN
SOMEWHAT WITHIN THE WARM SECTOR AND ALONG THE STATIONARY FRONTAL
BOUNDARY ACROSS VA/NC. GIVEN RICH LOW LEVEL MOISTURE AND SPC
MESOANALYSIS STILL INDICATING 500 J/KG TO NEAR 1000 J/KG MIXED
LAYER CAPE SOUTH OF THE FRONT...ONGOING CONVECTION IS LIKELY TO BE
MAINTAINED SEVERAL MORE HOURS. SOME WEAKENING MAY OCCUR OVER TIME
AS THE RAP DOES PREDICT DECREASING CAPE VALUES AFTER DARK...BUT
UNTIL THIS HAPPENS FLOODING AND FLASH FLOODING MAY CONTINUE TO
WORSEN THROUGH 02Z OR 03Z.
AT 22Z UPDRAFTS WERE CONGEALING AHEAD OF A WEAKLY DEFINED MCV AND
TRAILING SHORTWAVE TROUGH EXTENDING FROM HALIFAX VA INTO NORTHERN
NORTH CAROLINA. STEERING FLOW WILL TAKE THIS MCV AND ASSOCIATED
MID LEVEL FORCING NORTH TO NORTHEASTWARD ALONG THE FRONT. THE
FLASH FLOOD RISK SHOULD REMAIN ENHANCED THIS EVENING FROM HALIFAX
TO NEAR RICHMOND...FOLLOWING THE FRONTAL BOUNDARY...WHILE SHORTER
LIVED HEAVY DOWNPOURS ARE POSSIBLE FARTHER SOUTH INTO THE WARM
SECTOR AS CELLS FORM AND LIFT TO MERGE INTO THE FRONTAL ZONE. THE
12Z NAM CONUS NEST AND NSSL WRF DEPICT THIS QUITE WELL.
MUCH OF THIS REGION HAD RECEIVED 2 TO 6 INCHES OF RAIN OVER THE
PAST TWO DAYS. THE HYDROLOGIC RESPONSE MAY ESCALATE...INCLUDING ON
LONG AND SHORT TIME SCALES / FLASH FLOODING. RECENT REPORTS OF
BOTH DEBRIS FLOWS AND SINK HOLES WERE NOTED OUT OF SOUTHERN
VIRGINIA. DANGEROUS FLASH FLOODING IS LIKELY...ESPECIALLY EARLY
THIS EVENING.
BURKE
ATTN...WFO...AKQ...LWX...RAH...RNK...
ATTN...RFC...MARFC...SERFC...
LAT...LON 38197801 38067687 37817636 37267623 36357723
35727902 36047946 36657952 37537916
Last Updated: 631 PM EDT FRI MAY 18 2018