MESOSCALE PRECIPITATION DISCUSSION 0098
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1239 AM EDT SAT APR 14 2018

AREAS AFFECTED...FAR EAST TX...EASTERN AR...NORTHERN LA...WESTERN
MS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 140435Z - 140805Z

SUMMARY...CONVECTION ALONG AN AXIS OF DEEP MOISTURE AND
INSTABILITY IS EXPECTED TO PRODUCE FLASH FLOODING ACROSS PORTIONS
OF EASTERN AR INTO NORTHERN LA AND WESTERN MS INTO THE EARLY
MORNING HOURS.

DISCUSSION...NEWLY DEVELOPING CONVECTION OVER SOUTH CENTRAL AR
INTO NORTH CENTRAL LA IS TAKING ADVANTAGE OF AN AXIS OF 1000-2000
J/KG OF MUCAPE AND WAS EXPANDING LATE THIS EVENING. THE GOES-16
CLEAN IR LOOP SHOWED RAPID COOLING TOPS WITH THE NEW
CONVECTION...REACHING NEAR -70 C OVER SOUTH CENTRAL AND SOUTHEAST
AR. THE NEW CONVECTION IS PRODUCING HOURLY RAINFALL RATES NEAR
1.50 INCHES OVER THIS AREA.

THE NEW ACTIVITY IS AHEAD OF THE MAIN AXIS OF CONVECTION
STRETCHING FROM SOUTHEAST MO INTO EAST TX. A MERGER OF THE TWO
CONVECTIVE AXES IS EXPECTED OVER EASTERN AR AND NORTHERN AR
BETWEEN 14/0430Z AND 14/0515Z...BEFORE IT TRACKS EASTWARD INTO
WESTERN MS AND FAR WESTERN TN.

ONCE THE CONVECTIVE LINES MERGE...THEY WILL TAP 1.75 INCH
PRECIPITABLE WATER AIR TO PRODUCE HOURLY RAINFALL RATES NEAR 1.50
INCHES...WITH THE HIGHEST AMOUNTS EXPECTED OVER SOUTHERN
AR/NORTHERN LA...CLOSEST TO THE BEST INSTABILITY. WHILE THE
CONVECTION IS EXPECTED TO MOVE STEADILY EASTWARD (A MITIGATING
FACTOR FOR A MORE WIDESPREAD FLASH FLOOD THREAT)...THERE SHOULD BE
SUFFICIENT TRAINING OF INDIVIDUAL CELLS ALONG THE LINE TO PRODUCE
LOCAL 3.00 TO 5.00 INCH RAINFALL AMOUNTS (PER THE MOST RECENT HRRR
AND THE 00Z WRF ARW).

HOWEVER...IT SHOULD BE NOTED THAT MUCH OF THE AVAILABLE HIGH
RESOLUTION GUIDANCE IS AN HOUR OR SO SLOW WITH THE CONVECTION...
AND THE SIZE OF THE MPD WAS EXPANDED TO ACCOMMODATE THE SLOW MODEL
TIMING. IN ADDITION...THE RELATIVE SPEED OF THE CONVECTIVE LINE
COULD MAKE REALIZING THE MAXIMUM QPF AMOUNTS IN THE HIGH
RESOLUTION MORE DIFFICULT TO ATTAIN.

THREE HOUR FLASH FLOOD VALUES OVER THIS AREA ARE FAIRLY HIGH
(GENERALLY BETWEEN 2.00 AND 3.00 INCHES)...SO TRAINING WOULD BE
NEEDED TO INITIATE FLASH FLOODING. HOWEVER...GIVEN THE RAINFALL
AMOUNTS FROM THE LATEST HRRR AND THE 00Z WRF ARW...FLASH FLOODING
IS LIKELY THROUGH THE EARLY MORNING HOURS.

HAYES

ATTN...WFO...HGX...JAN...LCH...LZK...MEG...SHV...

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

LAT...LON   35999111 35809010 35198960 34289011 31369271
            31399497 32049518 35059295 35819175