MESOSCALE PRECIPITATION DISCUSSION 0592
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
329 AM EDT SAT JUL 29 2017

AREAS AFFECTED...SOUTHWESTERN PA/NORTHERN WV/NORTHERN VA/CENTRAL
TO SOUTHERN MD/DC/DE/SOUTHERN NJ...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 290728Z - 291328Z

SUMMARY...FLASH FLOODING WILL REMAIN LIKELY ACROSS MUCH OF THE MPD
AREA GIVEN SATURATED SOILS AND THE EXPECTATION OF ADDITIONAL HEAVY
RAINFALL OVERNIGHT. THIS SYSTEM HAS A HISTORY OF PRODUCING FLASH
FLOODING CONDITIONS ACROSS THE CENTRAL APPALACHIANS EASTWARD INTO
DC/MD/VA.

DISCUSSION...THE 07Z SURFACE ANALYSIS INDICATED A WAVE OF LOW
PRESSURE MOVING SOUTH OF DC WITH STRONG CONVERGENCE ALONG THE
ATTENDANT FRONTAL BOUNDARIES. WARM/MOIST AIR CONTINUES TO SURGE
POLEWARD IN ADVANCE OF THIS CYCLONE PUMPING 2 TO 2.25 INCH PWAT
VALUES INTO THE DELMARVA REGION. WIDESPREAD WARM-TOPPED CONVECTION
CONTINUES GENERALLY ALONG AND NORTH OF THE STATIONARY BOUNDARY
EXTENDING FROM SOUTHERN MD INTO SOUTHERN DE/NJ. INTENSE HOURLY
RAINFALL RATES WERE OBSERVED IN THE PROXIMITY OF BALTIMORE MD WITH
2 TO 2.50 INCHES ON THE MESONET. A DISTINCT DRY SLOT IS SEEN ON
RADAR/EXPERIMENTAL GOES-16 SATELLITE IMAGERY WHICH SHOULD AFFORD A
BREAK FROM THE ACTION FROM DC WESTWARD INTO MUCH OF MD AND
NORTHERN VA. FARTHER UPSTREAM...A PERSISTENT CONVECTIVE CLUSTER
HAS CONTINUED TO PRODUCE A NUMBER OF FLASH FLOODS ACROSS WESTERN
PA/NORTHERN WV. THIS IS IN RESPONSE TO FORCING WITH A SLOW MOVING
UPPER TROUGH CURRENTLY ABOUT TO EXIT FAR EASTERN OH. EVENTUALLY
THIS SHOULD SLIDE TOWARD THE SOUTH AND EAST POTENTIALLY MOVING
INTO REGIONS WHICH JUST RECEIVED HEAVY RAINFALL ON FRIDAY.

MANY OF THE HIGH-RESOLUTION MODELS WERE TOO SLOW IN BRINGING THE
DRY SLOT INTO THE DC METRO AREA. AN EVENTUAL LULL IS NOTED IN MOST
OF THE GUIDANCE THOUGH WITH THE 06Z HRRR/03Z EXPERIMENTAL HRRR
BEING MOST IN LINE WITH CURRENT RADAR TRENDS. WHILE THE CENTER OF
THE OUTLINED MPD WILL GENERALLY BE ON THE DRIER SIDE THROUGH
12Z...THINGS COULD PICK UP BY EARLY/MID-MORNING WITH THE
APPROACHING SHORTWAVE.


RUBIN-OSTER

ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...RLX...

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

LAT...LON   40297988 39727929 39437866 39237797 39197705
            39517590 39987485 39687400 39217390 38807416
            38467470 38257527 38017640 37997837 38427994
            39018050 39738072 40268054