Graphic for MPD #0013

MESOSCALE PRECIPITATION DISCUSSION 0013
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
435 PM EST SAT FEB 10 2018

AREAS AFFECTED...CTRL AND SRN APPALACHIAN REGION

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

VALID 102130Z - 110330Z

SUMMARY...PERSISTENCE OF RAIN OVER THE CENTRAL AND SOUTHERN
APPALACHIAN REGION SHOULD CONTRIBUTE TO A RISK OF FLOODING INTO
THE EVENING HOURS. 6-HOUR RAINFALL TOTALS ON THE ORDER OF 1-2
INCHES MAY PRODUCE LOCALIZED AREAS OF FLASH FLOODING.

DISCUSSION...MODEL FORECASTS PROJECT A RELATIVELY STEADY-STATE
MESOSCALE ENVIRONMENT ACROSS THE APPALACHIAN REGION INTO THE
EVENING HOURS. THE 19Z RAP SHOWS A PROMINENT AXIS OF BOUNDARY
LAYER CONVERGENCE STRETCHING FROM ROUGHLY HSV... TO CSV... TO
LNP... TO CHO... AND HAS THAT FEATURE PERSISTING IN APPROXIMATELY
THE SAME LOCATION THROUGH 03Z. IT IS THEREFORE UNSURPRISING THAT
THE BEST MODEL QPF SIGNAL IN THAT TIME FRAME STRETCHES FROM NRN
ALABAMA NORTHEASTWARD INTO THE CUMBERLAND MOUNTAINS REGION OF FAR
ERN KY... FAR WRN VA...AND SERN WEST VIRGINIA. AND REGIONAL RADARS
CONTINUE TO SHOW A LARGE RIBBON OF MODERATE TO OCCASIONALLY HEAVY
RAIN PUSHING INTO THE SAME AREAS. A LACK OF INSTABILITY WAS
KEEPING THE RAIN LARGELY NON-CONVECTIVE...BUT SMALL BANDS HAVE
OCCASIONALLY PRODUCED RAINFALL RATES UP TO 0.5 IN/HR.

DESPITE LOWER HOURLY RAIN RATES...THE CHANCES OF FLOODING
DEVELOPING ON 3 TO 6 HOUR TIME SCALES ARE CONSIDERABLY HIGHER.
6-HOUR FLASH FLOOD GUIDANCE IS QUITE LOW FROM MIDDLE TENNESSEE AND
SRN/ERN KENTUCKY INTO MUCH OF WEST VIRGINIA AND VIRGINIA. IN
FACT...THE 6HR FFG IS AROUND OR LESS THAN AN INCH ALONG MUCH OF
THE WV-VA BORDER REGION FROM BECKLEY WV NORTHEAST TO NEAR FRONT
ROYAL VA. THE NATIONAL WATER MODEL INITIALIZATION AT 20Z ALSO
SHOWS STREAMFLOW ABOVE NORMAL TO MUCH ABOVE NORMAL IN THE SAME
AREA.

GIVEN THE LOW FFG VALUES...THE 1-2 INCHES OF RAINFALL FROM 21-03Z
ON THE LATEST HREF BLENDED MEAN WOULD SUPPORT THE RISK OF FLASH
FLOODING ACROSS PORTIONS OF THE APPALACHIAN REGION. THE MOST
FAVORABLE OVERLAP OF HEAVIER QPF ON THE HREF...AND THE LOWER FFG
VALUES...APPEARS TO BE FROM THE KY-VA BORDER NORTHEAST INTO SRN
WV. THE HREF PROBABILITY OF EXCEEDING 1 INCH IN 6 HOURS IN THE
SAME AREA IS IN EXCESS OF 70 PERCENT. IN THESE MOUNTAINOUS
AREAS...SATURATED SOILS AND AT LEAST SEVERAL MORE HOURS OF STEADY
MODERATE TO OCCASIONALLY HEAVY RAIN MAY PRODUCE SOME MUD OR ROCK
SLIDES AS WELL...AND A MUDSLIDE HAS ALREADY BEEN REPORTED IN
BUCHANAN COUNTY VA. ALTHOUGH THE HREF DOES DEPICT SOME HIGHER
TOTALS OVER NRN AL AND SERN TN...FFG IN THOSE AREAS IS HIGHER AND
MAY LIMIT THE EXTENT OF ANY FLOODING THAT FAR SOUTH.

LAMERS

ATTN...WFO...BMX...FFC...GSP...HUN...JKL...LWX...MRX...OHX...
RLX...RNK...

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

LAT...LON   38817957 38597931 38197909 37897896 37477934
            37237994 36908019 36588049 36368107 36408166
            36348216 36158283 35908327 35688313 35498315
            35368338 35118333 34988347 35078381 35128417
            35068443 34948478 34578503 34428552 34268636
            34908688 35768614 36408505 37058423 37558330
            37978225 38358125 38558057 38798004


Last Updated: 435 PM EST SAT FEB 10 2018