MESOSCALE PRECIPITATION DISCUSSION 0646
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
228 PM EDT MON AUG 07 2017

AREAS AFFECTED...SOUTHERN NJ...DE...EASTERN MD...CENTRAL AND
EASTERN VA

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

VALID 071830Z - 080030Z

SUMMARY...SURFACE LOW/VORT CENTER TO TRACK OVER AREAS ALREADY
AFFECTED BY FLOODING RAINS ACROSS S NJ/DELMARVA.  TRAILING COLD
FRONT MAY ORIENT FAVORABLY FOR BACKBUILDING/TRAINING CELLS ACROSS
S VA THROUGH THE EVENING.

DISCUSSION...GOES-16 WV LOOP DEPICTS STRONG SHORTWAVE CROSSING
INTO N VA/CENTRAL MD WITH IMPRESSIVE BAROCLINIC LEAF ACROS SE
PA/NJ ATTM.  THIS IS SUPPORTING DEEPENING SURFACE WAVE THAT IS
TAKING SHAPE NEAR WASHINGTON DC WITH A LINE OF SHALLOW WARM TOPPED
CONVECTION TRAILING ALONG THE COLD FRONT.  IN ADVANCE OF THE
DEEPENING LOW...STRONG BAROCLINIC FORCING FROM SLY FLOW UP THE
CHESAPEAKE AND BACKING ONSHORE FLOW OFF THE NJ/DE/DELMARVA COAST
PROVIDE STRONG MST CONVERGENCE INTO DEFORMATION ZONE NEAR NAK TO
DOV TO JUST E OF PHL.  THIS MST FLUX WILL CONTINUE TO PROVIDE
HIGHLY EFFICIENT RAINFALL PRODUCTION...PARTICULARLY IN REMAINING
CONVECTIVE ELEMENTS THAT WILL PERSIST WITH STRONG WAA TRANSPORTING
INSTABILITY FROM THE SOUTH AND EAST FOR AT LEAST A FEW MORE HOURS.
AN ADDITIONAL 1-2" WILL CONTINUE TO KEEP FLASH FLOODING LIKELY. 

IF CLOUD DECK FROM DPVA ASCENT WITH MID-LEVEL SHORTWAVE EVACUATES
AS SUGGESTED BY CURRENT TREND...SOME SOLAR INSOLATION MAY ALLOW
SFC TEMPS TO REBOUND AFTER 21Z-00Z OVER S NJ/DELMARVA.  LOW LEVEL
FORCING WILL BE STRONG ENOUGH THROUGH ISALLOBARIC COMPONENT TO
CONVECT ANOTHER ROUND OVER SATURATED AREAS.  THIS EVOLUTION IS A
BIT LESS CERTAIN BUT WOULD ONLY FURTHER LEAD TO CONTINUED FLASH
FLOOD THREAT ACROSS NORTHERN/CENTRAL DELMARVA INTO S NJ. 

EAST CENTRAL VA/S DELMARVA...
MODERATELY CLEAR SKIES THROUGHOUT THE DAY HAVE SUPPORTED FILTERED
SOLAR INSOLATION ENOUGH TO SUPPORT A BUILD UP OF INSTABILITY WITH
1000-1250 J/KG OF MLCAPE SUPPORTED BY THE RAP ANALYSIS.  WHILE
MAIN SHORTWAVE ALOFT HAS TRANSITION THROUGH THE TERRAIN OF N
VA...THERE IS A TRAILING TROF HUNG UP ACROSS S WV CONNECTED BACK
TO S/W OVER CENTRAL TN.  THIS HAS ORIENTED FLOW TO BE FAIRLY
UNIDIRECTIONAL ACROSS S VA TO S TIP OF MD/S DELMARVA AND
EVENTUALLY WILL BE PARALLEL TO THE ORIENTATION OF THE COLD FRONT
SLOW DROPPING SOUTH FROM N VA.

SUFFICIENT SFC MST CONVERGENCE SHOULD SUPPORT CONVECTION TO
DEVELOP AND WITH 40KTS OF 850MB INFLOW FROM THE SOUTHWEST PAIRED
WITH MEAN 8-4H WINDS OF SIMILAR DIRECTION/MAGNITUDE SUPPORTS
NEARLY BACKBUILDING ENVIRONMENT ALONG WITH TRAINING TO POSE RISK
OF TRAINING WITH RATES UP TO 2-2.5"/HR.  AT THIS TIME PRECISE
LOCATION OF THESE TRAINING/BACKBUILDING CELLS IS DIFFICULT TO
DETERMINE EVEN WITH HI-RES GUIDANCE...YET WHERE THEY DO DEVELOP
THE POTENTIAL FOR 2-4" POSSIBLY HIGHER POSES A LEAST A POSSIBLE
FLASH FLOOD RISK THROUGH THE EVENING HOURS. 

GALLINA

ATTN...WFO...AKQ...LWX...PHI...RNK...

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

LAT...LON   39977500 39867467 39617409 38807478 37977513
            37147585 36987728 36867912 37347960 37767838
            38217763 38937681 39187644 39447614 39617578