MESOSCALE PRECIPITATION DISCUSSION 0951
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1030 PM EST FRI DEC 22 2017

AREAS AFFECTED......SOUTHERN AND EASTERN AR ACROSS NORTHERN MS
INTO WESTERN TN/WESTERN KY...

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

VALID 230330Z - 230930Z

SUMMARY...ADDITIONAL SHOWERS AND EMBEDDED THUNDERSTORMS WILL
PRODUCE LOCALLY HEAVY RAINFALL OVER AREAS WITH LOW FLASH FLOOD
GUIDANCE...CONTINUING THE THREAT FOR FLASH FLOODING INTO THE EARLY
MORNING HOURS.

DISCUSSION...REGIONAL RADARS CONTINUED TO SHOW SHOWERS AND
EMBEDDED CONVECTION TRACKING ACROSS AR...FAR NORTHWEST MS...
WESTERN TN INTO FAR WESTERN KY. MUCH OF THE ACTIVITY WAS NORTH OF
A STATIONARY FRONT STRETCHED ACROSS THE SAME REGION...AND
INSTABILITY NEAR AND NORTH OF THE FRONT WAS FAIRLY LIMITED (BASED
ON 00Z SOUNDINGS AT KLZK AND KBNA)...SO THE SHOWERS AND ELEVATED
CONVECTION WERE PRODUCING MAXIMUM  HOURLY RAINFALL RATES NEAR 0.50
INCHES.

SOUTH OF THE FRONT...WHERE THE MOST RECENT RAP ANALYSIS SHOWED
MUCAPE VALUES BETWEEN 500-1000 K/KG OVER SOUTHERN AR/NORTHERN AR
INTO CENTRAL MS (THE 00Z KSHV SOUNDING SHOWED SBCAPE VALUES NEAR
1200 J/KG). A 35 TO 45 KNOT LOW LEVEL SOUTHWEST FLOW (PER REGIONAL
VWP) CONTINUES TO FEED 1.50 INCH PRECIPITABLE WATER AIR (WHICH IS
ABOVE TWO STANDARD DEVIATIONS ABOVE THE MEAN) ALONG AND OVER THE
FRONT. IN THE WARM SECTOR SOUTH OF THE FRONT...KNQA RADAR SHOWED
HOURLY RAINFALL RATES CLOSER TO AN INCH.

THE FLOW BECOMES INCREASINGLY DIFFLUENT AS A 130/150 KNOT JET
STREAK EXITS THE LOWER MS VALLEY INTO THE UPPER MS VALLEY. THE
SYNOPTIC SCALE ASCENT IS EXPECTED TO ALLOW THE SHOWERS AND
EMBEDDED CONVECTION TO EXPAND ACROSS THE THE REGION. ALONG AND
NORTH OF THE FRONT...WHERE HOURLY RAINFALL RATES REMAIN BELOW
0.50/0.75 INCHES...THE MAIN THREAT IS FLOODING VERSUS FLASH
FLOODING...DUE TO THE LONG DURATION OF MODERATE RAINFALL RATES.

SOUTH OF THE FRONT...MAINLY ACROSS EASTERN AR...FAR NORTHWEST MS
INTO WESTERN TN/WESTERN KY...DEVELOPING CONVECTION MAY BE ABLE TO
TAP THE INSTABILITY UPSTREAM... PRODUCING HOURLY RAINFALL RATES
OVER AN INCH FOR A TIME BETWEEN 04Z AND 07Z. THE MOST RECENT
HRRR/EXPERIMENTAL HRRR SOLUTIONS SHOWED THE POTENTIAL FOR LOCAL
2.00 TO 3.00 INCHES OF RAINFALL FROM CENTRAL AR INTO WESTERN
TN/SOUTHWEST KY.

ONE AND THREE HOUR FLASH FLOOD VALUES FROM SOUTH CENTRAL AR INTO
FAR NORTHWEST MS AND SOUTHWEST TN ARE BELOW AN INCH...DUE TO
RECENT HEAVY RAINFALL. THESE AREAS WILL BE MORE PRONE TO FLASH
FLOODING INTO THE EARLY MORNING HOURS.

HAYES

ATTN...WFO...JAN...LMK...LZK...MEG...OHX...PAH...

ATTN...RFC...ABRFC...LMRFC...OHRFC...

LAT...LON   37658630 37308564 36818590 34898886 34818900
            33539148 33589296 34399349 36478996 36948884