MESOSCALE PRECIPITATION DISCUSSION 0284
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 PM EDT SUN JUN 10 2018

AREAS AFFECTED...CENTRAL/NORTHERN VA...D.C...MD...DE

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 102025Z - 110225Z

SUMMARY...SHOWERS AND THUNDERSTORMS WILL TEND TO BECOME A BIT MORE
WIDESPREAD OVER THE NEXT FEW HOURS. SOME FLASH FLOODING IS
POSSIBLE GIVEN THE HEAVY RAINFALL RATES AND WET ANTECEDENT
CONDITIONS.

DISCUSSION...RADAR IMAGERY SHOWS AN EXPANSIVE AREA OF MODERATE TO
LOCALLY HEAVY RAIN ACROSS CENTRAL AND SOUTHEAST PA...WITH AN AXIS
OF SCATTERED THUNDERSTORMS FARTHER SOUTH FROM NORTHEAST MD
SOUTHWEST DOWN ACROSS CENTRAL AND WESTERN VA.

A REMNANT MCV IS ADVANCING EAST ACROSS CENTRAL PA...AND SO FAR THE
BETTER FORCING HAS BEEN FOCUSED NORTH OF THE MAIN POOL OF
INSTABILITY OVER THE MID-ATLANTIC WHICH IS MOST DOMINANT DOWN NEAR
A QUASI-STATIONARY FRONTAL ZONE DRAPED OVER THE CENTRAL
APPALACHIANS AND DOWN ACROSS CENTRAL TO SOUTHEAST VA.

HOWEVER...OVER THE NEXT COUPLE OF HOURS...THERE MAY BE A BIT
BETTER JUXTAPOSITIONING OF THE INSTABILITY WITH MORE FAVORABLE
FORCING ALOFT. THERE SHOULD BE AT LEAST SOME MODEST RIGHT-ENTRANCE
REGION JET DYNAMICS SETTLING SOUTH ACROSS THE MID-ATLANTIC REGION
COURTESY OF AN UPPER JET AND ASSOCIATED TROUGH CUTTING ACROSS NEW
ENGLAND LATE THIS AFTERNOON AND EVENING. THIS COUPLED WITH A
GRADUAL POOLING OF MORE FAVORABLE...ALBEIT MODEST...INSTABILITY
FARTHER NORTH TOWARD THE NORTHERN VA/CENTRAL MD AREA AND ADJACENT
D.C. AND BALTIMORE METRO AREAS AND IN VICINITY OF THE FRONT WILL
RESULT IN SOMEWHAT MORE WIDESPREAD CONVECTIVE POTENTIAL.

PWATS ACROSS THE REGION ARE QUITE HIGH AT 1.7 TO 1.8 INCHES WHICH
WILL CONTRIBUTE TO HIGHLY EFFICIENT RAINFALL PRODUCERS AND INTENSE
RAINFALL RATES. KSHD JUST LAST HOUR ALONE REPORTED 2.22 INCHES OF
RAIN FROM A THUNDERSTORM...AND THESE EFFICIENT RATES CAN BE
EXPECTED THROUGH THE EVENING.

THE MODEL SIGNAL IS SOMEWHAT NEBULOUS AS TO WHERE EXACTLY THE
HEAVIEST RAINFALL POTENTIAL WILL SET UP...BUT THE LATEST THINKING
IS THAT AREAS NEAR THE FRONT WILL HAVE THE GREATEST POTENTIAL
GIVEN THIS IS WHERE THE BEST INSTABILITY GRADIENT IS RELATIVE TO
WHERE THE BETTER FORCING IS ALOFT.

EXPECT LOCALLY AS MUCH AS 2 TO 4 INCHES OF RAIN THROUGH
MID-EVENING WHERE THE STRONGER CONVECTIVE CORES SET-UP OR
CONCENTRATE. GIVEN THE ENHANCED SHORT-TERM RAINFALL RATES AND WET
ANTECEDENT CONDITIONS...SOME FLASH FLOODING IS POSSIBLE.

ORRISON

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

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

LAT...LON   39727656 39597570 38897526 38217553 37627655
            37337746 37317858 37587927 37967954 38427939
            38907880 39257807 39517750