MESOSCALE PRECIPITATION DISCUSSION 0711
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT THU SEP 29 2016
 
AREAS AFFECTED...CENTRAL/NORTHERN VA...DISTRICT OF
COLUMBIA...CENTRAL/SOUTHERN MD...DELMARVA PENINSULA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 290700Z - 291300Z
 
SUMMARY...HEAVY RAINS EXPECTED THROUGH DAWN WITH CONCERNS FOR
LOCALLY ENHANCED RUNOFF AND/OR FLASH FLOODING.

DISCUSSION...HEAVY RAINS ARE EXPECTED TO CONTINUE EARLY THIS
MORNING ACROSS PORTIONS OF CENTRAL/NORTHERN VA...THE DISTRICT OF
COLUMBIA...CENTRAL/SOUTHERN MD AND THE DELMARVA AS INCREASING
SOUTHEAST ATLANTIC INFLOW IN THE 925/850 MB LAYER CONTINUES TO
FOCUS ENHANCED MOISTURE CONVERGENCE AND FLUX ANOMALIES WHILE
MAINTAINING AN ELEVATED INSTABILITY GRADIENT NORTH OF A STATIONARY
FRONT OVER SOUTHEAST VA. THE LATEST WV/IR SATELLITE IMAGERY SHOWS
AN IMPRESSIVELY DIFFLUENT SIGNATURE OVER THE MID-ATLANTIC COASTAL
PLAIN WHICH IS SUGGESTIVE OF LARGER SCALE ASCENT OVER THE REGION.
MEANWHILE...PLENTY OF COLDER CONVECTIVE CLOUD TOPS ARE SEEN...WITH
THE STRONGEST CORES OVER THE DELMARVA WHICH HAVE BEEN ASSOCIATED
WITH SOME SLOW-MOVING DISCREET CELLS ASSOCIATED WITH OVERSHOOTING
TOPS.

THE HIRES GUIDANCE IS DOING RATHER POORLY OVERALL HANDLING THE
CONVECTION OVER CENTRAL AND SOUTHERN VA...WHILE DOING BETTER WITH
THE ACTIVITY FARTHER NORTHEAST TOWARD SOUTHERN MD AND THE
DELMARVA. THE EXPECTATION IS THAT CONVECTION EAST OF AN INVERTED
TROUGH EXTENDING NORTH INTO NORTHERN VA AND NORTHEAST OF A WAVE OF
LOW PRESSURE SHOULD TEND TO BE SUSTAINABLE AT LEAST THROUGH 12Z
CONSIDERING THE DEGREE OF LOW LEVEL JET ENERGY THAT IS FORECAST BY
RECENT RUNS OF THE RAP TO SET UP OVER THE REGION. MEANWHILE...THIS
WILL BE AIDED BY LARGE SCALE DIVERGENT FLOW ALOFT AROUND THE
EASTERN FLANK OF AN UPPER LOW DROPPING SOUTH OVER THE OH VALLEY.

PWATS ARE INCREASING AND SHOULD REACH OVER 1.75 INCHES NEAR AND
EAST OF I-95. SO THIS WILL CONTINUE TO FAVOR EFFICIENT RAINFALL
PROCESSES THAT WILL SUPPORT RAINFALL RATES AS HIGH AS 2.5
INCHES/HR WITHIN THE STRONGER CONVECTIVE CORES AND ESPECIALLY WITH
ANY OVERSHOOTING TOP ACTIVITY.

GIVEN HEAVY RAINS EARLIER ON WEDNESDAY AND WITH ADDITIONAL HEAVY
RAINFALL POTENTIAL EXPECTED PAST DAWN...THE THREAT FOR RUNOFF
PROBLEMS AND/OR FLASH FLOODING WILL PERSIST. WHILE AREAL AVERAGE
AMOUNTS WILL PROBABLY BE ON THE ORDER OF 1 TO 2 INCHES...EXPECT
LOCALLY AS MUCH AS AN ADDITIONAL 3 TO 5 INCHES OF RAIN WITHIN
AREAS OF PERSISTENT AND/OR REPEATING ACTIVITY THROUGH DAWN. THIS
IS SUPPORTED BY RECENT HRRR/HRRR EXPERIMENTAL GUIDANCE.

ORRISON

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

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

LAT...LON   39727619 39527544 38897502 38507491 38087512 
            37787544 37287631 37147697 37357768 37587782 
            37877783 38397778 38797769 39187756 39467739 
            39647706