MESOSCALE PRECIPITATION DISCUSSION 0099
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
405 AM EDT SAT APR 14 2018

AREAS AFFECTED...EASTERN AR...WESTERN MS...WESTERN TN

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

VALID 140805Z - 141405Z

SUMMARY...CELLS TRAINING ALONG A CONVECTIVE LINE MOVING ACROSS
AR/LA/WESTERN MS AND WESTERN TN THIS MORNING ARE EXPECTED TO
PRODUCE FLASH FLOODING.

DISCUSSION...THE CONVECTIVE LINE EXTENDING ACROSS EASTERN AND
SOUTH CENTRAL AR INTO FAR NORTHERN AR CONTINUES TO FEED ON
1000-2000 J/KG OF MUCAPE AS IT MOVES SLOWLY EASTWARD EARLY THIS
MORNING. A 40 TO 60 KNOT LOW LEVEL SOUTH SOUTHWEST FLOW PUMPS 1.75
INCH PRECIPITABLE WATER AIR (WHICH IS BETWEEN TWO AND THREE
STANDARD DEVIATIONS ABOVE THE MEAN) OVER LA/EASTERN AR INTO
WESTERN MS/WESTERN TN.

THE STRONGEST CONVECTION OVER EAST CENTRAL AR IS ACCOMPANIED BY
BURSTS OF COLDER CLOUD TOPS...WITH TEMPERATURES BOTTOMING OUT NEAR
-73 CELSIUS. SLOWLY INCREASING MID AND UPPER LEVEL DIVERGENCE IS
EVIDENT IN THE GOES-16 CLEAN IR LOOP...AS A CLOSED MID LEVEL LOW
OVER KS/NE TRUNDLES EASTWARD. ALONG THE AXIS OF DEEPEST
MOISTURE...THE KLZK RADAR INDICATED HOURLY RAINFALL RATES IN
EXCESS OF 2.00 INCHES OVER CLEVELAND... LINCOLN AND ARKANSAS
COUNTIES. SOME OF THIS COULD BE HAIL CONTAMINATED...AS MID LEVEL
LAPSE RATES CONTINUE TO STEEPEN AHEAD OF THE FRONT.

THE BEST INSTABILITY AND LOW LEVEL MOISTURE FLUX IS EXPECTED
THROUGH ABOUT 14/12Z ACROSS EASTERN AR INTO NORTHWEST MS AND
WESTERN TN. THE MOST RECENT RAP SHOWED THE INSTABILITY RETREATING
TOWARD SOUTHERN LA/MS...AND THE STRONG LOW LEVEL WINDS STARTING
EASE OFF AND VEER. BEFORE 14/12Z HOWEVER...THE LATEST HRRR/00Z
CONUS NAM NEST (WHICH HAVE HAD THE BEST HANDLE ON THE MOVEMENT OF
THE CONVECTIVE LINE THUS FAR) SHOWED THE POTENTIAL FOR 3.00 TO
5.00 INCHES OF RAINFALL OVER EAST CENTRAL AR INTO FAR NORTHWEST MS
AND FAR WESTERN TN.

GIVEN WHAT HAS OCCURRED IN THE QUASI UNIDIRECTIONAL FLOW THUS
FAR...THESE AMOUNTS SEEM PLAUSIBLE. THE RELATIVELY FAST MOVEMENT
OF THE CONVECTIVE LINE AHEAD OF THE FRONT...AND THE RELATIVELY
HIGH THREE HOUR FLASH FLOOD GUIDANCE VALUES (GENERALLY ABOVE
2.50/2.00 INCHES) COULD END UP BEING MITIGATING FACTORS FOR A MORE
EXTENSIVE FLASH FLOOD EVENT.

AFTER 14/12Z...WITH WANING INSTABILITY... THE CONVECTION MAY TEND
TO BOW OUT ACROSS WESTERN TN AND NORTHERN MS. THE THREAT FOR
ADDITIONAL FLASH FLOODING SHOULD DWINDLE AFTER THAT TIME.

HAYES

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

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

LAT...LON   36938772 35608806 33199029 32839118 32939147
            33129167 33709188 34749140 36448985