MESOSCALE PRECIPITATION DISCUSSION 0213
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
208 AM EDT TUE AUG 13 2013
 
AREAS AFFECTED...MD...DE...WEST NJ...SE PA...NORTH VA...SE
OH...NORTH WV 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 130546Z - 131146Z
 
SUMMARY...WIDESPREAD THUNDERSTORMS EXPECTED. INDIVIDUAL CELL
MOTIONS RELATIVELY QUICK...BUT EXPECT AREAS OF TRAINING TO COMBINE
WITH HIGH RAIN RATES TO MAKE FLASH FLOODING LIKELY.

DISCUSSION...STORMS WERE ALREADY TRAINING ACROSS OH/WV. THIS AND
THE AREA DOWNSTREAM TO THE MID ATLANTIC WILL BE WITHIN A FAVORABLE
WARM ADVECTION REGIME IN THE ENTRANCE OF A 90 KT 250 MB JET. CELLS
HAD BEEN BUBBLING OVER NORTHERN VA MUCH OF THE EVENING...AND
EXPECT THESE TO INTENSIFY AS UPGLIDE BECOMES FOCUSED PER NAM AND
GFS FORECASTS. REFERENCE 305 K LEVEL ON AWIPS BASED ON ROANOKE
SOUNDING IN THE INFLOW SOURCE REGION. WARM ADVECTION BECOMES
MARKED OVER MD/DE AND SOUTHEAST PA BY 09-12Z...SO ANTICIPATE A
SHIFT TOWARD GREATER STORM COVERAGE IN THESE AREAS...WHILE
COVERAGE OVER OH/WV SHOULD BEGIN TO DECREASE DURING THAT SAME TIME
WITH A 700 MB WAVE PUSHING THROUGH.

GIVEN THE MODERATE SYNOPTIC SCALE FORCING HERE...THE GLOBAL MODELS
WILL PROBABLY VERIFY WELL WITH THE AREAL OUTLINE OF HEAVIER QPF.
NOW THE 00Z HIGH RESOLUTION MODELS HAVE ALSO COME INTO GOOD
AGREEMENT IN HIGHLIGHTING SWATHS OF HEAVY RAIN BETWEEN 06-12Z. ONE
CONSENSUS AXIS IS ACROSS NORTHERN MD AND ADJACENT DE/NJ TO THE
EAST...AND ANOTHER AXIS DEVELOPS UP TOWARD NORTHEAST PA...PERHAPS
FORCED BY UPGLIDE IN A MORE ELEVATED LAYER. MUCH OF THE HIGH RES
GUIDANCE IS ALSO HEAVY ACROSS EAST-CENTRAL VA AND SE MD. DESPITE
BEING SOUTH OF THE SFC WARM FRONT...THIS AREA WILL SEE A LOW LEVEL
SURGE...WITH MODELS SHOWING A SELDOM SEEN EARLY MORNING INCREASE
OF CAPE.

ASIDE FROM THE WV MOUNTAINS AND URBAN AREAS TO THE EAST...THE
FLASH FLOOD GUIDANCE IS RATHER HIGH...AND MOTION FOR ORDINARY
CELLS PREDICTED AT A GOOD 20-25 KT. BUT SHEAR PROFILES FAVOR SOME
UPDRAFT ROTATION...PER SPC DAY 1 OUTLOOK...AND BUNKERS SUPERCELL
MOTION WILL BE SLOWER...EAST AT 10-15 KT. GIVEN SETUP FOR
EFFICIENT RAIN PRODUCERS...NOTING RECENT 1.5-2.0 INCH/HOUR RATES
VIA WFO RLX...WOULD EXPECT SOME QUICK 2-4 INCH TOTALS WHEREVER
TRAINING DEVELOPS.

BURKE

ATTN...WFO...PHI...BGM...AKQ...CTP...LWX...PBZ...RLX...ILN...

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

LAT...LON   40267951 40817800 41327688 41477547 41127493 40287488
            39577500 38187554 37467633 37597705 38307847 38277983
            38508153 39048265 39658221 40267951