MESOSCALE PRECIPITATION DISCUSSION 0581
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
941 AM EDT FRI JUL 28 2017

AREAS AFFECTED...SOUTHERN OH...CENTRAL/EASTERN KY...SOUTHWEST
VA...CENTRAL/WESTERN WV...EXTREME SOUTHWEST PA

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

VALID 281340Z - 281940Z

SUMMARY...SHOWERS AND THUNDERSTORMS WITH VERY HEAVY RAINFALL RATES
ARE EXPECTED TO DEVELOP AND EXPAND IN COVERAGE OVER THE NEXT FEW
HOURS. RAINFALL RATES OF UP TO 2.5 INCHES/HR ARE EXPECTED...AND
FLASH FLOODING WILL BE A THREAT.

DISCUSSION...THE LATEST EXPERIMENTAL GOES-16 6.9 MICRON/WV AND
RGB/AIRMASS IMAGERY SHOWS A SIGNIFICANT SHORTWAVE TROUGH RAPIDLY
AMPLIFYING ACROSS THE LOWER GREAT LAKES REGION...WITH A CLOSED 500
MB CENTER ALREADY DIGGING SOUTHEAST ACROSS NORTHERN LOWER MI.
MEANWHILE...UPSTREAM OVER SOUTHERN WI...THERE IS A SIGNIFICANT
AMOUNT DRYING/DARKENING SEEN IN THE WV IMAGERY WHICH IS
CORRESPONDING TO A 90+KT 250 MB JET MAX THAT IS DIGGING SOUTHEAST
IN TOWARD THE BASE OF THE AMPLIFYING TROUGH.

ALL OF THIS ENERGY IS RAPIDLY ENCROACHING ON THE OH VALLEY AND
CENTRAL APPALACHIANS WHERE A FRONTAL ZONE IS SLOWLY PUSHING EAST
ALONG WITH MULTIPLE WAVES OF LOW PRESSURE. ALONG AND SOUTH OF THIS
FRONT IS A VERY MOIST AIRMASS WITH PWATS OF GENERALLY 1.8 TO 2.0
INCHES AND WITH MODEST INSTABILITY AS CHARACTERIZED BY MUCAPE
VALUES OF 500 TO 1000 J/KG.

OVER THE NEXT FEW HOURS...STRENGTHENING DPVA AND DIVERGENT FLOW
ALOFT WILL BE INTERACTING WITH THE FRONT AND WITH THE AIRMASS OUT
AHEAD OF IT FOR NUMEROUS SHOWERS AND THUNDERSTORMS TO DEVELOP. AN
INCREASE IN DIURNAL HEATING ALONG WITH SOME OROGRAPHIC FORCING
WILL ALSO FACILITATE THE INCREASED COVERAGE OF CONVECTION.

EXPECT RAINFALL RATES TO BE QUITE INTENSE...PERHAPS REACHING AS
HIGH AS 2.5 INCHES/HR WITHIN THE STRONGER CONVECTIVE CORES. THIS
COUPLED WITH RELATIVELY SLOW CELL MOTION SHOULD FOSTER SOME VERY
HEAVY RAINFALL TOTALS THROUGH MID-AFTERNOON. THE 00Z ARW/NMMB
GUIDANCE AND ESPECIALLY RECENT HRRRX RUNS SUPPORT AS MUCH AS 3 TO
5 INCHES OF RAIN. FLASH FLOODING IS LIKELY WITH THESE TOTALS AND
ESPECIALLY CONSIDERING SOME OF THE RECENT RAINFALL ACROSS THE
REGION AND LOCALLY RUGGED TERRAIN. WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...CTP...ILN...JKL...LMK...LWX...MRX...PBZ...RLX...
RNK...

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

LAT...LON   39948045 39757896 39097891 38267931 37558009
            36888162 36648321 36708463 37318564 38008593
            38738545 39118456 39248338 39508222