MESOSCALE PRECIPITATION DISCUSSION 0050
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
750 PM EST TUE FEB 27 2018

AREAS AFFECTED...SOUTHERN AND CENTRAL AR...NORTHERN MS...WESTERN
TN

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

VALID 280100Z - 280700Z

SUMMARY...ELEVATED CONVECTION IN A HIGH MOISTURE ENVIRONMENT COULD
RESULT IN FLASH FLOODING OVER WET SOILS INTO THE EARLY MORNING
HOURS.

DISCUSSION...CONVECTION CONTINUES ALONG AN ELEVATED BOUNDARY
EXTENDING FROM SOUTHERN AR INTO NORTHWEST MS THIS EVENING. THE
CONVECTION IS FOLLOWING AN AXIS OF 100-250 J/KG OF MUCAPE (PER THE
MOST RECENT SPC MESOANAYLSIS) EXTENDED ALONG THE ELEVATED
BOUNDARY. A PLUME OF DEEP MOISTURE (WITH BOTH THE MOST RECENT RAP
ANALYSIS AND LATEST BLENDED TPW SHOWING PRECIPITABLE WATER VALUES
BETWEEN 1.50 AND 1.75 INCHES...WHICH IS NEAR THREE STANDARD
DEVIATIONS ABOVE THE MEAN)...ORIGINATING OVER THE EASTERN
PACIFIC...FEEDS THE ELEVATED CONVECTION. THE KSHV RADAR EARLIER
SHOWED HOURLY RAINFALL RATES NEAR 1.00 INCHES OVER NORTHERN
LA...AND GIVEN THE DEPTH OF MOISTURE IN THE PLUME...THOSE VALUES
SEEM REASONABLE.

THE DEEP MOISTURE PLUME REMAINS FOCUSED ON THE ELEVATED
INSTABILITY AXIS/BOUNDARY INTO THE EARLY MORNING HOURS...PER THE
MOST RECENT RAP. A WEAK MID LEVEL SHORT WAVE IS EXPECTED TO CROSS
AR INTO NORTHERN MS...AND LIFT WITH THE SHORT WAVE COULD HELP KEEP
THE ELEVATED CONVECTION AT LEAST SOMEWHAT ORGANIZED...AS IT MOVES
EAST NORTHEAST IN A BROAD WARM AIR ADVECTION PATTERN.

THE MOST RECENT HRRR/EXPERIMENTAL HRRR (AS WELL AS THE 12Z NSSL
WRF) HAVE HANDLED THE CONVECTION FAIRLY WELL THUS FAR...TAKING THE
HIGHEST RAINFALL AMOUNTS ACROSS NORTHERNMOST LA INTO SOUTHERN AR.
THESE SOLUTIONS SUGGEST THAT THE HIGHEST RAINFALL AMOUNTS WITH THE
ELEVATED CONVECTION OCCUR IN THE 01Z TO 06Z TIME FRAME ACROSS
SOUTHEAST AR INTO NORTHERN MS AND FAR SOUTHWEST TN...WITH LOCAL
2.00 INCH RAINFALL AMOUNTS.

IT SHOULD BE NOTED THAT BOTH HRRR SOLUTIONS HAVE BEEN SLOW WITH
THE CONVECTION. AT ANY RATE...THE HIGHER RAINFALL AMOUNTS ARE
EXPECTED OVER AREAS WHERE THE MOST RECENT HRRR SOIL SATURATION
PRODUCT SHOWED NEARLY SATURATED SOILS EXTENDING FROM SOUTHERN AR
INTO WEST CENTRAL MS. THE ADDITIONAL RAINFALL COULD RESULT IN AN
FLASH FLOOD THREAT INTO THE EARLY MORNING HOURS.

HAYES

ATTN...WFO...JAN...LZK...MEG...SHV...

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

LAT...LON   35768950 35578879 34868832 33818848 33118992
            32959156 33049252 33499327 34539330 35349188