MESOSCALE PRECIPITATION DISCUSSION 0509
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EDT SUN JUL 22 2018
AREAS AFFECTED...CENTRAL MD...NORTHERN VA...
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 221745Z - 222230Z
SUMMARY...INCREASINGLY EFFICIENT CONVECTION NEAR MCV LIFTING
THROUGH WET ANTECEDENT SOIL CONDITIONS POSE POSSIBLE FLASH
FLOODING RISK.
DISCUSSION...REMOTE SENSING SUITE FROM GOES-16 AND RADAR MOSAIC
DEPICT A COMPACT MCV LIFTING THROUGH NOVA AT THIS TIME HEADING
NNW. SFC MESO ANALYSIS DEPICTS RETURNING WARM FRONT ACROSS THE
NORTHERN NECKS OF TIDEWATER VA INTO ST. MARY'S COUNTY MD BEFORE
ANGLING EASTWARD TOWARD TALBOT COUNTY. STRONG SELY FLOW UP THE
CHESAPEAKE INTO THE POTOMAC RIVER HAS INCREASED TO 20-25KTS PER
MESO OBSERVATIONS WHILE ABOUT 10KTS IN ST.MARY'S COUNTY. THIS IS
PROVIDING MODERATE WAA AND MST CONVERGENCE ALONG THE EASTERN SIDE
OF THE MCV'S MID-LEVEL CONFLUENCE TO SPARK DEEPER CONVECTION.
WHILE GOES-16 IR SHOWS TOPS COOLING TO -45C...THIS SHALLOW WARM
CLOUD PROCESS WITH LIMITED LIGHTNING STRIKES SUGGEST INCREASED
RAINFALL EFFICIENCY FOR THESE CELLS WITH RADAR ESTIMATES NEARING
1.5"/HR WHICH SEEM PLAUSIBLE GIVEN THE AMPLE MOISTURE UP IN THE
MID-70S AT THE SFC AND TOTAL PWATS UP TO 1.75".
WHILE CELL MOTIONS ARE FAIRLY QUICK TO THE NORTH WITH FAIRLY
UNIDIRECTIONAL SOUTHERLY CLOUD BARING FLOW SUPPORTING 25-30KT
MOTIONS. THE ANGLE TO THE UPSTREAM MST CONVERGENCE ALONG THE
NORTHERN NECK AND INTO SE MD SUGGEST A BACKBUILDING ENVIRONMENT
EXISTS TO SUPPORT SOME TRAINING ACROSS CENTRAL MD OVER THE NEXT
FEW HOURS UNTIL BEST MID-LEVEL FORCING IS WELL REMOVED. AS SUCH
2-3" TOTALS COULD BE EXPECTED ESPECIALLY OVER SOUTHERN MD. CELLS
TRACKING A BIT MORE WEST OF DUE NORTH COULD POSE URBAN ISSUES
THOUGH WITH DISTANCE REMOVAL FROM THE BEST INSTABILITY/ASCENT
RAINFALL EFFICIENCY MAY BE SLIGHTLY REDUCED. GREATER RISK FOR
BACKBUILDING IS LIKELY TO BE ACROSS S VA INTO NE NC...BUT THERE IS
A SUFFICIENT THREAT ACROSS CENTRAL MD GIVEN ANTECEDENT CONDITIONS
THAT FLASH FLOODING MAY BE POSSIBLE IN THE NEXT 1-3 HOURS.
GALLINA
ATTN...WFO...AKQ...CTP...LWX...PHI...
ATTN...RFC...MARFC...
LAT...LON 39777695 39477644 38717637 37907617 37837669
38357714 38667729 39367753 39697735
Last Updated: 145 PM EDT SUN JUL 22 2018