MESOSCALE PRECIPITATION DISCUSSION 0435
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
515 AM EDT MON JUL 03 2017

AREAS AFFECTED...NORTHEAST AR ...FAR SOUTHEAST MO...FAR WESTERN TN

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

VALID 030915Z - 031445Z

SUMMARY...DEEP MOISTURE AND INSTABILITY STREAMING AHEAD OF A
LONG-LIVED MCV COULD RESULT IN A FLASH FLOOD THREAT THIS MORNING.

DISCUSSION...RADAR AND SATELLITE LOOPS SHOWED THE LONG-LIVED AND
STRONG MCV CROSSING INTO NORTHWEST AR EARLY THIS MORNING. AHEAD OF
THE MCV...500-1000 J/KG OF MUCAPE AND PRECIPITABLE WATER VALUES
NEAR 2.00 INCHES ARE BEING TRANSPORTED NORTHEAST ON A 25 TO 35
KNOT LOW LEVEL SOUTHWEST FLOW. MUCH OF THE CONVECTION AHEAD OF THE
MCV HAS BECOME OUTFLOW DOMINATED...WHICH IS AIDING TO MITIGATING
THE FLASH FLOOD THREAT AT LEAST IN THE NEAR TERM.

HOWEVER...THE MOISTURE AND INSTABILITY HAVE BECOME FOCUSED ON A
LOW LEVEL BOUNDARY STRETCHED ACROSS NORTHERN AR INTO WESTERN
TN...AND IS BEST DELINEATED BY AN ISODROSOTHERMAL GRADIENT. ALONG
THIS GRADIENT...PROPAGATION VECTORS HAVE DROPPED TO NEAR 10 KNOTS
OR SO...AND THIS IS ALLOWING CONVECTION TO SLOW ACROSS NORTHEAST
AR INTO FAR SOUTHEAST MO AND FAR WESTERN TN. BOTH THE LZK AND NQA
RADARS HAVE SHOWN HOURLY RAINFALL RATES NEAR 1.75 INCHES...WHERE
TRAINING HAS BEEN OCCURRING.

AS THE MCV MOVES EASTWARD...THE BEST THRUST OF MOISTURE AND
INSTABILITY IS EXPECTED TO BECOME FOCUSED ALONG THE DEW POINT
GRADIENT THROUGH ABOUT 14Z. INTERESTINGLY...WHILE THE LATEST RAP
AND HRRR RUNS HAVE THE FORCING IN THE RIGHT LOCATIONS...NEITHER IS
HANDLING THE CONVECTION ON THE DEW POINT GRADIENT WELL AT ALL.

IN FACT...MUCH OF THE AVAILABLE HIGH RESOLUTION GUIDANCE IS TOO
FAR WEST WITH THE RAINFALL...AND THIS WAS ADJUSTED TO BETTER FIT
THE CURRENT RADAR TRENDS. ONE AND THREE HOUR FLASH FLOOD GUIDANCE
VALUES ARE GENERALLY BETWEEN 2.00 AND 3.00 INCHES ACROSS NORTHEAST
AR INTO WESTERN TN. HOWEVER...TRAINING IN THE HIGH MOISTURE
CONTENT AIR SHOULD RESULT IN AN EXPANSION OF THE THREAT OF FLASH
FLOODING THROUGH ABOUT 15Z.

HAYES

ATTN...WFO...LZK...MEG...PAH...SGF...

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

LAT...LON   36719074 36658932 36168855 35298870 34619089
            34759186 35859225