MESOSCALE PRECIPITATION DISCUSSION 0062
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
936 AM EDT SUN MAR 18 2018

AREAS AFFECTED...CTRL AND SE LOUISIANA...SRN MISSISSIPPI

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

VALID 181335Z - 181930Z

SUMMARY...CLUSTER OF THUNDERSTORMS WILL PUSH EAST OR SOUTHEAST
THROUGH THE REMAINDER OF THE MORNING AND INTO THE EARLY AFTERNOON.
RAIN RATES AS HIGH AS 2 IN/HR WILL BE POSSIBLE AND COULD LEAD TO
FLASH FLOODING.

DISCUSSION...REGIONAL RADARS AND GOES-EAST IR SATELLITE SHOWED A
CLUSTER OF THUNDERSTORMS BEGINNING TO CONSOLIDATE AND ORGANIZE
JUST SOUTHWEST OF ALEXANDRIA LA...AND MOVING INTO RAPIDES PARISH
AS OF 1315Z. OBJECTIVE ANALYSIS INDICATES AROUND 500 J/KG OF
MUCAPE AND 0-6KM BULK SHEAR AROUND 40-45 KNOTS...A FAVORABLE
ENVIRONMENT FOR STORMS TO CONTINUE TO ORGANIZE AND PERSIST AS THEY
PUSH TO THE EAST-SOUTHEAST ON THE NOSE OF BROAD LOW-LEVEL INFLOW.
THE THUNDERSTORMS ALSO APPEARED TO BE ORGANIZING JUST EAST OF A
SURFACE MESOLOW PER SURFACE WIND OBSERVATIONS AND A RELATIVE
MINIMUM IN MSLP AROUND FORT POLK LA (KPOE). EXTENDING TO THE ESE
IS A GRADIENT IN SURFACE THETAE WITH SOME WEAK CONFLUENCE NOTED IN
THE SURFACE WIND OBSERVATIONS. THIS IS LIKELY A MESOSCALE
BOUNDARY...AND AS IT FAVORABLY ALIGNS WITH THE NOSE OF THE LLJ
SHOULD PROVIDE A FOCUS FOR CONVECTIVE GROWTH AND PROPAGATION OF
THE CONVECTIVE CLUSTER IN WEST-CENTRAL LOUISIANA. SURFACE
DEWPOINTS TO THE SOUTH OF THE BOUNDARY ARE AROUND 70 AND SOME
BREAKS IN THE LOW CLOUDS WERE NOTED ON VISIBLE SATELLITE. THIS MAY
ALLOW FOR INCREASING INSTABILITY THROUGH THE MORNING...SHARPEN THE
LOW-LEVEL THETAE GRADIENT...AND PROVIDE INCREASING FOCUS FOR HEAVY
RAINFALL INTO THE EARLY AFTERNOON.

HI-RES MODEL GUIDANCE GENERALLY SHOWS A SIGNAL FOR A SWATH OF
HEAVIER RAINFALL IN PARTS OF SE LOUISIANA AND PERHAPS FAR SW
MISSISSIPPI. THE 06Z HREF PROBABILITY MATCHED MEAN HAS 2-4 INCH
ACCUMULATIONS OVER 6 HOURS FROM POINTE COUPEE PARISH SOUTHEAST TO
THE VICINITY OF LAKE PONCHARTRAIN...AND INDIVIDUAL MEMBERS SHOW
MAXIMUM RATES AROUND 2 IN/HR. MRMS AND KPOE RADAR DUAL POL
ESTIMATES HAVE ALREADY REACHED THAT HIGH IN PORTIONS OF VERNON AND
RAPIDES PARISH...AND THE EXPECTATION IS THAT SHOULD CONTINUE
FURTHER EAST AND/OR SOUTHEAST. THOSE RATES...COMBINED WITH
LOW-TOPPED CONVECTION IN THE MOIST UNSTABLE INFLOW MERGING IN
AHEAD OF THE PRIMARY CONVECTIVE CLUSTER...SHOULD LEAD TO A THREAT
OF FLASH FLOODING AND LOCALIZED RAINFALL TOTALS AT LEAST
APPROACHING 3-4 INCHES IN A COUPLE HOURS IN NARROW BANDS.

LAMERS

ATTN...WFO...JAN...LCH...LIX...MOB...SHV...

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

LAT...LON   31778907 31488853 30628840 30058864 29658936
            29609037 29899112 30209172 30479238 30719305
            30989333 31449287 31539159 31758990