MESOSCALE PRECIPITATION DISCUSSION 0515...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
612 PM EDT SUN JUL 22 2018

CORRECTED FOR FLASH FLOODING LIKELY IN CONCERNING LINE

AREAS AFFECTED...SOUTHEAST PA...CENTRAL MD...EXT NORTHERN VA...EXT
NORTHERN DE...

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

VALID 222158Z - 230145Z

SUMMARY...A COUPLE OF COMPLEXES FED BY SWLY ONSHORE FLOW FOCUSED
BY RIVERS POSE LIKELY FLASH FLOODING ACROSS SE PA TO CENTRAL MD
OVER THE NEXT FEW HOURS.

DISCUSSION...MCV LIFTING INTO CENTRAL PA CONTINUES TO HAVE AN
ACTIVE CONVECTIVE COMPLEX ALONG THE EASTERN PERIPHERY OF ITS
INFLUENCE IN SE PA/EXT NE MD AND N DE ATTM. STRONG SFC FLOW UP THE
DELAWARE RIVER AND SLIGHT TURNING AT THE APEX OF THE CHESAPEAKE
BAY LEADING TO VERY STRONG MST CONVERGENCE AND BACKBUILDING GIVEN
STRONGER INFLOW AT THE EDGE OF THE MID-LEVEL TROF/CONFLUENCE BAND.
 THIS ALSO INTERSECTS GENERALLY WITH THE WARM FRONT THAT CONTINUES
HANG THROUGH SE PA INTO ANNE ARUNDEL COUNTY MD INTO THE PIEDMONT
REGION OF VA.

STRONG MST CONVERGENCE ALONG THE WARM FRONT IS SUPPORTING
CONVECTIVE DEVELOPMENT ALONG ITS LENGTH INTO VA BUT GIVEN THE
STUBBORN NATURE OF THE RIDGING OVER WEST CENTRAL MD INTO NW
VA...THERE CONTINUES TO BE SLOW NNW MOVEMENT OF THE FRONT ALLOWING
FOR BACKBUILDING ALONG THE UPSTREAM EDGE AND COMPOUNDING RAINFALL
TOTALS DOWNSTREAM.  THE BEST TRAINING REMAINS WHERE THE FRONT IS
MORE PARALLEL TO THE MEAN FLOW ACROSS SOUTHERN MD TOWARD BALTIMORE
CITY.  IN ADDITION ANOTHER SUBTLE S/W WILL HAS INCREASED WAA
ACROSS THE NORTHERN NECK OF VA LIFTING NORTH SUPPORTING A BAND OF
CONVECTION THAT WILL LIKELY BE ENHANCED BY THIS PARALLEL NATURE TO
THE FRONT AND THE INCREASED LOW LEVEL FLUX/CONVERGENCE CONTINUING
THE FLASH FLOOD THREAT FOR THE NEXT FEW HOURS ALONG THE LENGTH OF
THE CHESAPEAKE BAY.

AMPLE MOISTURE WITH TPWS STILL OVER 1.75" AND INSTABILITY FED ON
UNCLOUDED SOURCE REGION WILL SUPPORT RATES UP TO 1.75"/HR (AS
OBSERVED RECENTLY IN CALVERT COUNTY) BUT GIVEN OVERALL FORWARD
PROGRESS TOTALS SHOULD BE AROUND 2-4" THOUGH ISOLATED HUNG UP
CELLS NEAR/DOWNSTREAM OF FRICTIONAL CONVERGENCE POINTS NEAR THE
BAY/RIVERS...MAY SEE INCREASED TOTALS.  WITH LOW FFG VALUES FLASH
FLOODING IS CONSIDERED LIKELY.

GALLINA

ATTN...WFO...AKQ...CTP...LWX...PHI...

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

LAT...LON   40817557 40577526 40057515 39507582 38887623
            38507637 38097633 38027640 38157681 38307718
            38447741 38817758 39397753 39787732 40357677
            40597649 40807609