MESOSCALE PRECIPITATION DISCUSSION 0106
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
907 PM EDT SUN APR 15 2018

AREAS AFFECTED...CENTRAL VA...NORTHERN CENTRAL MD...DC

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

VALID 160010Z - 160410Z

SUMMARY...CELLS TRAINING ALONG A CONVECTIVE LINE MOVING SLOWLY
EAST ACROSS THE MID ATLANTIC STATES POSE THE THREAT FOR FLASH
FLOODING INTO THE EARLY MORNING HOURS.

DISCUSSION...REGIONAL RADARS SHOWED A CONVECTIVE LINE STRETCHING
FROM CENTRAL VA SOUTH TO THE SOUTHEAST NC COAST THIS EVENING. THE
LINE OF CONVECTION IS FEEDING ON THE WESTERN EDGE OF A MUCAPE
GRADIENT OF 250/500 J/KG EXTENDING WESTWARD INTO CENTRAL
VA/CENTRAL NC. REGIONAL VWP INDICATED LOW LEVEL WINDS HAVE
INCREASED TO 50 TO 70 KNOTS (THE 15/00Z KGSO SOUNDINGS SHOWED 60
KNOT AT 850 MB).

THE VERY STRONG LOW LEVEL FLOW CONTINUES TO PUMP 1.50 INCH
PRECIPITABLE WATER AIR (PER 00Z SOUNDINGS IN THE MID ATLANTIC...AS
WELL AS THE MOST RECENT RAP ANALYSIS). AS CELLS ALONG THE LINE
CONTINUE TO TRACK NORTH NORTHEAST ALONG THE LINE AS IT MOVES
SLOWLY EASTWARD...SHORT TERM TRAINING IS OCCURRING UPSTREAM IN
CENTRAL NC. THE KRAX RADAR SHOWED HOURLY RAINFALL RATES AS HIGH AS
1.50 INCHES. ALL OF THIS SETS THE STAGE FOR A CONTINUATION OF
SHORT TERM TRAINING OF CELLS IN A HIGH MOISTURE ENVIRONMENT. THE
MOST RECENT RAP SHOWED THE LOW LEVEL FLOW BECOME MORE CONVERGENT
WITH TIME...AS WINDS INCREASE TO 75 KNOTS.

THE MOST RECENT HRRR SHOWED LOCAL 2.00 TO 3.00 INCHES OF RAINFALL
IN THE NEXT THREE HOURS...AS THE CELLS TRACK TO THE NORTH
NORTHEAST. THE CONVECTION WILL EVENTUALLY RUN OUT OF THE BEST
INSTABILITY...BUT THE LOW LEVEL CONVERGENCE AND DYNAMIC FORCING
AHEAD OF A NEGATIVELY TILTED MID LEVEL LOW COULD COUNTER THE LOSS
OF INSTABILITY TO MAINTAIN A FLASH FLOOD THREAT INTO THE EARLY
MORNING HOURS.

THE BEST THREAT FOR FLASH FLOODING IS EXPECTED OVER WESTERN AND
CENTRAL VA... WHERE THE FLASH FLOOD GUIDANCE IS LOWEST. FURTHER
EAST...FLASH FLOOD GUIDANCE IS HIGHER...WHICH COULD MITIGATE A
MORE WIDESPREAD FLASH FLOOD THREAT OVER PORTIONS OF NORTH CENTRAL
MD...AS WELL AS THE DCA AREA.

HAYES

ATTN...WFO...AKQ...CTP...LWX...RNK...

ATTN...RFC...MARFC...SERFC...

LAT...LON   39797708 39697684 39607675 39407667 39087666
            38397673 36837723 37307856 37457869 38057891
            38947864 39527824 39737788