Flash Flood Guidance
Issued by NWS

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000
AWUS01 KWNH 252352
FFGMPD
NJZ000-PAZ000-DEZ000-MDZ000-260400-

MESOSCALE PRECIPITATION DISCUSSION 0273
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
752 PM EDT THU MAY 25 2017

AREAS AFFECTED...FAR NORTHEAST MD..NORTHERN .DE...SOUTHEAST
PA...WESTERN NJ

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

VALID 252340Z - 260400Z

SUMMARY...TRAINING CONVECTION COULD RESULT IN A SHORT TERM FLASH
FLOOD THREAT THROUGH THE EVENING HOURS.

DISCUSSION...REGIONAL RADARS SHOWED A CONVECTIVE LINE MOVING NORTH
THROUGH NORTHERN MD AND SOUTHERN DE. THE MIDDLE OF THE
LINE...NEARING NORTHEAST MD...IS  ACCELERATING NORTHWARD AHEAD OF
A CLOSED MID LEVEL LOW OVER WESTERN VA.

THE CONVECTION IS MOVING THROUGH AN AREA OF 500-1000 J/KG OVER
THIS AREA...WHERE PRECIPITABLE WATER VALUES VALUES HAVE INCREASED
TO NEAR 1.25 INCHES AS THE LOW LEVEL INFLOW BACKS. THE KLWX RADAR
HAS INDICATED HOURLY RAINFALL RATES AS HIGH AS 2.00 INCHES...BUT
GIVEN THE DRY AIR IN THE MID LEVELS (PER RAP MODEL SOUNDINGS) AND
PRIOR SPOTTER REPORTS...THESE AMOUNTS COULD BE HAIL CONTAMINATED.

AS THE MID LEVEL CLOSED LOW TRACKS TOWARD NORTHERN VA THIS
EVENING...THE MID LEVEL FLOW BECOMES MORE UNIDIRECTIONAL
(SOUTHERLY) WITH TIME. THIS COULD ALLOW BULGE IN THE CURRENT
CONVECTION TO BECOME MORE NORTH/SOUTH ORIENTED. AS THE CONVECTION
BECOMES BETTER ALIGNED WITH THE MID LEVEL WINDS...TRAINING BECOMES
AN INCREASING POSSIBILITY.

THE LATEST HRRR (AND TO A LESSER EXTENT... THE EXPERIMENTAL
HRRR)...HAVE HAD A GOOD HANDLE ON THE CONVECTION THUS FAR. THESE
SOLUTIONS INDICATED LOCAL 1.50 TO 2.50 INCH RAINFALL AMOUNTS
ORIENTED NORTH/SOUTH ACROSS PORTIONS OF FAR NORTHERN DE...
SOUTHEAST PA AND NEARBY SOUTHWEST NJ (ESSENTIALLY ALONG THE
INTERSTATE 95 CORRIDOR).

ONE AND THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE CLOSE TO THESE
VALUES. TRAINING WOULD BE NECESSARY FOR FLASH FLOODING TO
OCCUR...WHICH BECOMES INCREASING POSSIBLE...ESPECIALLY OVER
SOUTHEAST PA AND PORTIONS OF SOUTHWEST NJ THROUGH THE LATE EVENING
HOURS.

HAYES

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...CTP...LWX...OKX...PHI...

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

LAT...LON   40717442 40517431 40377434 40257443 40127452
            39977460 39817470 39727477 39587487 39427505
            39227559 39387597 39627614 39827607 40127578
            40467535 40547525 40687486


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