MESOSCALE PRECIPITATION DISCUSSION 0012
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1048 AM EST SAT FEB 10 2018

AREAS AFFECTED...SRN/ERN KY...CTRL/ERN TN...SRN WV...FAR WRN
VA...NRN AL

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

VALID 101545Z - 102145Z

SUMMARY...THE CHANCES OF FLOODING WILL INCREASE INTO THE AFTERNOON
HOURS FROM THE TENNESSEE VALLEY INTO THE CUMBERLAND PLATEAU AND
NEARBY AREAS. RAIN RATES SHOULD GENERALLY BE AROUND 0.5 IN/HR OR
LESS...BUT SUSTAINED OVER 3-6 HOURS COULD PRODUCE SOME FLASH
FLOODING GIVEN ALREADY SATURATED SOILS.

DISCUSSION...REGIONAL RADARS AT 1530Z SHOWED A PLUME OF MODERATE
TO OCCASIONALLY HEAVY RAIN STRETCHING FROM NRN MISSISSIPPI TO AS
FAR NORTHEAST AS NRN VIRGINIA. THIS ARC OF RAIN WAS ANCHORED IN
THE AXIS OF HIGHER PWATS AND ALONG THE NOSE OF THE DEVELOPING
LOW-LEVEL JET. OBJECTIVE RAP ANALYSIS ALSO SHOWED A LONG RIBBON OF
ENHANCED BOUNDARY LAYER CONVERGENCE CO-LOCATED WITH THE RAIN...AND
THIS WAS SITUATED SOUTHEAST OF THE SYNOPTIC FRONT (ABOUT 150 MILES
TO THE NORTHWEST). AS HIGHER PWATS CONTINUE TO SURGE TO THE
NORTHEAST IN DEEP SOUTHWESTERLY FLOW INTO THE AFTERNOON
HOURS...THE AVERAGE POSITION OF THE MOISTURE AND LOW-LEVEL
CONVERGENCE AXIS SHOULD CHANGE VERY LITTLE AND THIS IS EXPECTED TO
SUSTAIN THE RAINFALL FROM NRN AL AND MIDDLE TN NORTHEASTWARD INTO
SRN/ERN KENTUCKY AND SRN WEST VIRGINIA.

THE LOWEST FLASH-FLOOD GUIDANCE VALUES IN THE OUTLINED AREA WERE
FROM NASHVILLE METRO ENE INTO SOUTHEAST KENTUCKY. 6-HOUR FFG WAS
ON THE ORDER OF 1-2 INCHES IN THIS CORRIDOR...WITH HRRR PERCENT
SOIL SATURATION (TOP 1 CM) GENERALLY ABOVE 80 PERCENT.
THEREFORE...ALTHOUGH HOURLY RAIN RATES SHOULD NOT BE EXCEPTIONALLY
HIGH...SUSTAINED MODERATE RAINFALL OVER 3-6 HOURS COULD EXCEED
FLASH FLOOD GUIDANCE AND WILL CONTRIBUTE TO A GRADUAL INCREASE IN
THE CHANCES FOR FLOODING ACROSS THE REGION INTO THE AFTERNOON
HOURS. A FEW LIGHTNING STRIKES HAVE BEEN OBSERVED IN NORTHERN
TENNESSEE IN THE 15Z HOUR...AND RAP ANALYSIS INDICATES MUCAPE
AROUND 100 J/KG OR SO. THEREFORE...IT IS NOT OUT OF THE QUESTION
THAT SOME SMALL BANDS OF HEAVIER RAIN COULD DEVELOP WITH RAIN
RATES THAT BRIEFLY EXCEED 0.5 IN/HR...AND THAT WOULD ONLY ENHANCE
THE RISK OF FLOODING.

BY LATER IN THE AFTERNOON (AFTER 20Z)...THE GREATER CHANCES FOR
FLOODING ARE EXPECTED TO BUILD INTO SERN KENTUCKY AND SURROUNDING
AREAS...AS THE NOSE OF THE STRONGEST 850MB MOISTURE TRANSPORT
BECOMES MOST FAVORABLY ALIGNED WITH THE REGION OF LOWEST FFG AND
RAP FORECASTS THE BNA PWAT TO APPROACH FEBRUARY RECORD LEVELS.

LAMERS

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

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

LAT...LON   37858195 37768080 37348084 37058156 36878267
            36598363 35808454 34948557 34398602 34068658
            34038719 34278775 34788802 35428780 36048725
            36558637 37038530 37488412 37758293