Graphic for MPD #0783

MESOSCALE PRECIPITATION DISCUSSION 0783
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT TUE SEP 05 2017

AREAS AFFECTED...SE KY...CTRL AND ERN TN...FAR WRN NC AND VA...SRN
WV

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

VALID 051557Z - 052057Z

SUMMARY...INCREASING CONVECTION LATE THIS MORNING AND THIS
AFTERNOON MAY PRODUCE UP TO 2 IN/HR RAIN RATES AND LOCALIZED FLASH
FLOODING.

DISCUSSION...SYNOPTIC COLD FRONT WAS PUSHING SOUTH AND EAST THIS
MORNING THROUGH THE OHIO RIVER VALLEY...AHEAD OF A DIGGING
SHORTWAVE ALOFT THAT SHOWS UP PROMINENTLY ON SATELLITE WATER VAPOR
CHANNELS AND THE GOES-16 AIR MASS RGB. THE DIGGING WAVE WILL
CONTRIBUTE TO A STRENGTHENING JET STREAK FROM ILLINOIS AND INDIANA
INTO THE ST. LAWRENCE RIVER VALLEY...AND A CORRESPONDING INCREASE
IN UPPER LEVEL DIVERGENCE IN THE RIGHT ENTRANCE REGION OVER
EASTERN KENTUCKY AND TENNESSEE AND SURROUNDING AREAS THIS
AFTERNOON. ONGOING CONVECTION OVER KY AND TN HAS BEEN SCATTERED
THUS FAR...BUT MAY INCREASE IN SPATIAL COVERAGE OVER THE NEXT
SEVERAL HOURS AS THE COLD FRONT CONTINUES TO ADVANCE AND UPPER
LEVEL SUPPORT FOR LARGER SCALE VERTICAL MOTION IMPROVES.

RAIN RATES WITH ONGOING CONVECTION HAS BEEN IN THE 1-2 IN/HR RANGE
WITH MORE ORGANIZED MULTICELL CLUSTERS...WITH GOOD AGREEMENT
BETWEEN INDIVIDUAL RADARS AND MRMS ESTIMATES...AS WELL AS SOME
SURFACE OBSERVING SITES FROM THE KY MESONET. THESE HAVE EVEN BEEN
OBSERVED WITH SOME THUNDERSTORMS BEHIND THE SURFACE COLD
FRONT...DEVELOPING WITH SOME ELEVATED INSTABILITY ON THE SLOPED
FRONTAL SURFACE IN THE 950-850MB LAYER. OVERALL THESE RAIN RATES
SHOULD BE A GOOD BENCHMARK FOR WHAT WILL BE ACHIEVABLE FOR THE
NEXT SEVERAL HOURS...AND IF THEY CAN BE SUSTAINED IN CERTAIN AREAS
FOR A COUPLE HOURS COULD LEAD TO FLASH FLOODING.

ONE POTENTIAL FOCUSING MECHANISM FOR MORE ORGANIZED CONVECTION AND
SUSTAINED HIGHER RAIN RATES WOULD BE A DEVELOPING DIFFERENTIAL
HEATING BOUNDARY FROM ROUGHLY KSYI TO KTYS IN EAST-CENTRAL
TENNESSEE. ONGOING RAIN AND DENSER CLOUD COVER TO THE NORTH OF THE
BOUNDARY IS GENERALLY RESTRICTING TEMPERATURES INTO THE UPPER 60S
WITH A LOOSELY ORGANIZED CONVECTIVE COLD POOL. MEANWHILE...TO THE
SOUTH TEMPERATURES HAVE BEEN RISING INTO THE LOWER 80S WITH
SURFACE DEWPOINTS FROM THE MID 60S TO LOWER 70S...AND RAP MODEL
FORECASTS SHOW INCREASING BOUNDARY LAYER MIXING RATIOS INTO THE
AFTERNOON HOURS. AS LOW-LEVEL FLOW BACKS SLIGHTLY AND INCREASES
AHEAD OF THE APPROACHING COLD FRONT...RENEWED CELL GROWTH MAY
OCCUR ON THE UPSHEAR FLANK OF THE COLD POOL...WITH CELL
PROPAGATION NEAR OR OVER AREAS THAT HAVE ALREADY RECEIVED RAINFALL
ALONG THE DIFFERENTIAL HEATING BOUNDARY. THIS BOUNDARY COINCIDES
WITH SLIGHTLY LOWER FLASH FLOOD GUIDANCE VALUES TO THE EAST OF THE
CUMBERLAND PLATEAU...AND MAY BE AN AREA OF GREATER FLASH FLOOD
THREAT WITHIN THE BROADER MPD AREA.

LAMERS

ATTN...WFO...FFC...GSP...HUN...JKL...LMK...MRX...OHX...RLX...
RNK...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   38288156 38268086 37898044 37508060 36978103
            36518138 35858209 35208339 34968445 34988552
            35208647 35568700 36128731 36748692 37118609
            37288525 37638418 37868312 38098213


Last Updated: 1159 AM EDT TUE SEP 05 2017