MESOSCALE PRECIPITATION DISCUSSION 0089
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1038 AM EDT FRI APR 06 2018

AREAS AFFECTED...EASTERN OK...AR...CENTRAL/NORTHERN MS

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

VALID 061435Z - 062035Z

SUMMARY...NUMEROUS SHOWERS AND THUNDERSTORMS WILL CONTINUE WELL
INTO THE AFTERNOON HOURS...WITH CONCERNS OF REPEATING CELL
ACTIVITY. FLASH FLOODING IS POSSIBLE.

DISCUSSION...THE LATEST RADAR IMAGERY SHOWS AN EXPANSIVE AXIS OF
ELEVATED CONVECTION STRETCHING FROM EASTERN OK EAST-SOUTHEAST
ACROSS CENTRAL AR AND INTO NORTHWEST MS. THE CONVECTION IS
INITIATING WITH A BROAD LOW TO MID LEVEL WARM AIR ADVECTION
PATTERN AHEAD OF A SOUTHERN PLAINS SHORTWAVE TROUGH THAT IS
ALLOWING DEEP MOISTURE TO FOCUS NORTH UP ACROSS THE LOWER MS
VALLEY IN CONJUNCTION WITH A GRADUAL INCREASE IN INSTABILITY. THE
CONVECTION OVER THE LAST SEVERAL HOURS HAS BEEN FOCUSING NORTH OF
A WARM FRONT AND WITHIN A FAIRLY WELL-DEFINED INSTABILITY GRADIENT
CHARACTERIZED BY MUCAPE VALUES OF 500 TO 1000 J/KG.

THE UPPER LEVEL FLOW IS RATHER DIFFLUENT AHEAD OF THE SHORTWAVE
TROUGH...AND OVER THE NEXT SEVERAL HOURS THE THERMODYNAMICS
ENVIRONMENT SHOULD BE CONDUCIVE FOR SUSTAINABLE CONVECTION THAT
WILL BE ALIGNED NORTH AND PARALLEL TO THE WARM FRONT...BUT ALSO
THE MEAN LAYER WIND VECTOR WHICH WILL FAVOR REPEATING CELL
ACTIVITY. THE PWATS ARE CURRENTLY AROUND 1.25 INCHES NEAR THE AXIS
OF CONVECTION AND SHOULD CONTINUE TO RISE TO NEAR 1.5 INCHES
THROUGH 18Z TO 21Z. THIS WILL FAVOR AN UPTICK IN RAINFALL RATES
THAT SHOULD RISE TO NEAR OR OVER 1.5 INCHES/HR WITHIN THE STRONGER
CONVECTIVE CORES.

SOIL SATURATION FIELDS BASED OFF THE HRRR GUIDANCE WHEN COUPLED
WITH FORECAST QPF SUGGESTS AN INCREASED THREAT OF RUNOFF PROBLEMS
GOING THROUGH THE EARLY TO MID-AFTERNOON HOURS...AND MAINLY GIVEN
THE REPEATING CONVECTIVE CELL POTENTIAL. EXPECT AS MUCH AS AN
ADDITIONAL 3 TO 4 INCHES OF RAIN THROUGH THIS TIME FRAME.
THEREFORE...SOME FLASH FLOODING WILL BE POSSIBLE.

ONE CONCERN IN TIME IS THAT THE CONVECTION WILL TEND TO BECOME
MORE ORGANIZED TO THE LEVEL OF CREATING A SUFFICIENT COLD POOL
THAT MAY ALLOW CONVECTION TO BEGIN SAGGING OR DEVELOPING FARTHER
SOUTH TOWARD THE WARM SECTOR. RECENT RUNS OF THE HRRR COUPLED WITH
THE OVERNIGHT ARW...NMMB AND ARW2 SOLUTIONS ALL FAVOR THIS. THUS
AREAS OF SOUTHERN AR...NORTHERN LA AND CENTRAL MS WILL EVENTUALLY
NEED TO BE MONITORED FOR HEAVY TO EXCESSIVE RAINFALL LATER TODAY.

ORRISON

ATTN...WFO...JAN...LZK...MEG...OUN...SHV...TSA...

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

LAT...LON   36179565 35899434 35209188 34618926 33718837
            32748901 32859024 33289185 33519325 34039504
            34619598 35399653 35969638