MESOSCALE PRECIPITATION DISCUSSION 0109
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 AM EDT MON APR 16 2018
AREAS AFFECTED...NORTHEAST MD ACROSS SOUTHEAST PA IN SOUTHEAST NY
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 160730Z - 161400Z
SUMMARY...CELLS TRACKING NORTH ALONG A LINE MOVING EAST IN A HIGH
MOISTURE ENVIRONMENT ACROSS THE NORTHERN MID ATLANTIC STATES POSE
A THREAT FOR FLASH FLOODING INTO THE MORNING HOURS.
DISCUSSION...REGIONAL RADARS CONTINUE TO TRACK A LINE OF
CONVECTION EXTENDING FROM SOUTH CENTRAL PA INTO EASTERN NC. THE
CONVECTION REMAINS ON THE WESTERN EDGE OF A MUCAPE GRADIENT ACROSS
CENTRAL VA INTO NORTHEAST MD...SOUTHEAST PA AND A PORTION OF
SOUTHWEST NJ. WHILE THE ACTIVITY REMAINS ELEVATED ON THE NORTH
SIDE OF A BOUNDARY EXTENDING ACROSS VA...THERE ARE LIGHTNING
STRIKES AS FAR NORTH AS NORTHERN MD.
THE MOST RECENT RAP ANALYSIS SHOWED A 60 TO 70 KNOT LOW LEVEL
SOUTH SOUTHEAST JET PUMPING 1.50 INCH PRECIPITABLE WATER AIR
(WHICH IS SUPPORTED BY THE MOST RECENT BLENDED TPW PRODUCT). TOPS
ON THE CONVECTION ARE COMPARATIVELY LOW...AS SEEN IN THE GOES-16
CLEAN IR CHANNEL...BUT GIVEN THE INSTABILITY IN PLACE...THAT IS
NOT UNEXPECTED. THE KLWX RADAR SHOWED HOURLY RAINFALL RATES AS
HIGH AS 1.50 INCHES OVER RICHMOND AND WESTMORELAND COUNTIES IN
VA... AND HOURLY MESONET OBSERVATIONS WERE GENERALLY IN THE
1.00/1.25 INCH RANGE.
LOCATIONS SOUTH AND WEST OF KDCA HAS RECEIVED BETWEEN 2.00 AND
3.00 INCHES OF RAINFALL WITH THE TRAINING CELLS ALONG THE LINE
EARLY THIS MORNING.
MOVING FORWARD...INSTABILITY AND THE EASTWARD TRACK OF THE
CONVECTIVE LINE WILL BE LIMITING FACTORS FOR A MORE WIDESPREAD
FLASH FLOOD THREAT. RAP SOUNDINGS ALONG THE INTERSTATE 95 CORRIDOR
SHOWED 100 TO 250 J/KG OF MUCAPE FROM NORTH OF KBWI TO SOUTH OF
KEWR. THE INSTABILITY SHOULD BE SUFFICIENT TO SUSTAIN THE
CONVECTION IN PLACE...AS THIS AREA MAY BRIEFLY GET INTO THE WARM
SECTOR...AND THE VERY STRONG AND CONVERGENT LOW LEVEL INFLOW IS
EXPECTED TO MAINTAIN RAINFALL RATES OCCASIONALLY REACHING OVER AN
INCH AN HOUR...ESPECIALLY OVER SOUTHEAST PA INTO NORTHERN NJ.
THE MOST RECENT HRRR HAD A GOOD HANDLE ON THE CONVECTION...BUT WAS
AN HOUR OR SO SLOW WITH ITS EASTWARD PROGRESS (WHICH WAS TYPICAL
OF MOST OF THE AVAILABLE HIGH RESOLUTION GUIDANCE). THE HRRR
SHOWED LOCAL 2.00 TO 3.00 INCH RAINFALL AMOUNTS IN THE
ABOVEMENTIONED LOCATIONS...AND BASED ON WHAT HAS OCCURRED SOUTH
AND WEST OF KDCA THIS MORNING...THOSE VALUES SEEM PLAUSIBLE.
ONE HOUR FLASH FLOOD VALUES ARE AS LOW AS 1.00/1.50 INCHES OVER
PORTIONS OF SOUTHEAST PA AND NORTHEAST NJ...MAKING THEM THE MOST
SUSCEPTIBLE TO FLASH FLOODING THIS MORNING. OTHERWISE...TRAINING
WILL BE REQUIRED TO INITIATE FLASH FLOODING...SO FLASH FLOODING IS
ONLY CONSIDERED POSSIBLE.
HAYES
ATTN...WFO...BGM...CTP...LWX...OKX...PHI...
ATTN...RFC...MARFC...NERFC...
LAT...LON 41507421 41327363 41027344 40737367 39387516
38967561 38727612 39007653 39947636 40547607
41467491
Last Updated: 328 AM EDT MON APR 16 2018