MESOSCALE PRECIPITATION DISCUSSION 0076
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
859 PM EDT TUE MAY 27 2014
 
AREAS AFFECTED...LA...FAR ERN TX...FAR WRN MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 280058Z - 280658Z
 
SUMMARY...LOCATION VARIES SLIGHTLY BUT ALL MODELS SIGNAL A HEAVY
RAIN EVENT. TRENDS IN THE HOURLY-UPDATING RAP AND HRRR GIVE US
SOME CONFIDENCE THAT THE EVENT WILL INITIATE OVER LOUISIANA
BETWEEN 02-07Z. TRAINING OF CELLS ALONG THE LEADING EDGE OF
UNSTABLE AIR COULD LEAD TO LOCAL FLASH FLOODING BY 05Z WITH THE
THREAT POSSIBLY INCREASING IN SCOPE AND MAGNITUDE THEREAFTER.

DISCUSSION...A RELATIVELY IDENTIFIABLE HEAVY RAIN EVENT IS
EXPECTED...AND IS REFLECTED IN WPC QPF AND EXCESSIVE RAINFALL
OUTLOOKS. MESOSCALE ASPECTS OF THE EVENT ARE STILL IN
QUESTION...BUT IT APPEARS SYNOPTIC FORCING WILL COUNTER THE
STABILIZING INFLUENCE OF THE DAYTIME SQUALL LINE AS EVIDENCED BY
THE 00Z KLCH RAOB. THE AREA NEAR/SOUTH OF THE 16 C ISOTHERM AT 850
MB SAW ONLY SHALLOW CONVECTION... RESULTING IN A POOL OF
MODERATELY UNSTABLE AIR TO BE ADVECTED INLAND. SUSTAINED MID LEVEL
ASCENT AHEAD OF THE TEXAS UPPER LOW...ALONG WITH UPPER JET LEVEL
WINDS THAT ARE SLIGHTLY DIFLUENT...AND MORE DIFLUENT WITH EASTWARD
EXTENT...WILL AID DEEP LAYER LIFT AND MAINTAIN LAPSE RATES
SUFFICIENT FOR DEEP CONVECTION.

WHILE THE MODELS ALL SIGNAL HEAVY RAIN IN A GENERAL
SENSE...CONFIDENCE IS INCREASED BY A TREND THAT DEVELOPED IN THE
20Z HRRR AND REMAINED SOLID IN THE 21...22Z RUNS. THESE POINT TO
PARTICULARLY HEAVY RAIN...LOCALLY 5-PLUS INCHES IN 6 HOURS IN THE
MODEL...IN CENTRAL LA BEGINNING 02-07Z. RAP TRENDS IN
TIMING/PLACEMENT ARE SIMILAR. GREATEST OVERLAP OF LOWER/MID LEVEL
ASCENT IS PREDICTED OVER LA...BUT SOME BACKBUILDING INTO THE LOW
LEVEL INFLOW IS POSSIBLE TOWARD TX...AS WELL AS SOME SPILL-OVER OF
ACTIVITY INTO MS.

BURKE

ATTN...WFO...JAN...LIX...LCH...SHV...HGX...

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

LAT...LON   32909012 32589106 31649256 30839403 30019506 29699523
            29289503 29119424 29279267 29749154 30829060 31749018
            32369003 32909012 
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