Flash Flood Guidance
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000
AWUS01 KWNH 300307
FFGMPD
MSZ000-LAZ000-300815-

MESOSCALE PRECIPITATION DISCUSSION 0087
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1107 PM EDT WED MAR 29 2017

AREAS AFFECTED...SOUTHERN LA...SOUTHWEST MS

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

VALID 300305Z - 300815Z

SUMMARY...MESO-LOW AND WEST TO EAST ORIENTED OUTFLOW ALONG WITH
CONTINUED STRONG ONSHORE FLOW SUPPORTS ENVIRONMENT FOR SLOW MOVING
HIGHLY EFFICIENT RAINFALL PRODUCING CELLS SUPPORTING CONTINUED
FLASH FLOODING THREAT THROUGH LATE NIGHT HOURS.

DISCUSSION...SIGNIFICANT LATENT HEAT RELEASE IN CONVECTIVE COMPLEX
ALONG WITH SPLIT JET STRUCTURE ALOFT HAS SUPPORTED THE GENERATION
OF A MODEST MCV THAT IS LIFTING ENE INTO SW MS ATTM PER RADAR
MOSAIC.  ADDITIONALLY THE COLD POOL GENERATION SUPPORTS A WEAKLY
DEFINED WEST TO EAST OUTFLOW BOUNDARY PARALLEL BUT JUST SOUTH OF
I-10.  WV LOOP SHOWS THE BROADLY DIFFLUENT PATTERN ALOFT THOUGH
SUBTROPICAL JET BREAKS EASTWARD ALONG THE NORTHERN GULF COAST
LEADING TO THE NICELY SPLIT JET AND GOES EIR SHOWS COMPLEX HAS
DEVELOPED A NICE WEDGE APPEARANCE WITHIN THE SPLIT.  THE MAIN
HEIGHT FALLS REMAIN UPSTREAM FOR A FEW MORE HOURS BEFORE THE
EASTWARD PUSH IS TO OCCUR...ADVANCING THE MAIN COLD FRONT
CURRENTLY ACROSS EASTERN TX.   AS SUCH SURFACE AND LOW LEVEL WIND
FLOW REGIMES CONTINUE TO TRANSPORT HIGH THETA-E WITH SURFACE
20-25KT SELY VEERING WITH HEIGHT TOWARD STRONG CONVERGENCE
BOUNDARY DEMARCATED BY GROWING CONVECTIVE LINE PARALLEL TO THE SE
TX COAST COMING ASHORE ACROSS LAKE CHARLES VICINITY.  BROAD SWLY
FLOW INTERSECTING WITH THE W-E OUTFLOW BOUNDARY SUPPORTS
ISENTROPIC ASCENT TO TAP ANY REMAINING ELEVATED INSTABILITY AND
CONTINUING TO CONTRIBUTE TO CONVECTIVE REDEVELOPMENT POST LEADING
EDGE OF TROF NEAR THE MESO-LOW.   THESE COMBINED FACTORS WILL
CONTINUE TO SUPPORT FLASH FLOODING CONDITIONS ACROSS SOUTH CENTRAL
LA LIFTING INTO SW MS WHERE RAINFALL RATES IN EXCESS AT OR ABOVE
2"/HR REMAIN LIKELY FOR THE NEXT FEW HOURS OR SO.

RAPID REFRESH HI-RES GUIDANCE PARTICULARLY THE HRRR AND ESRL EXP.
HURR AND RAP SUGGEST ARE NOT AS BROAD/AMPLIFIED WITH THE MESO LOW
AND MUCH SLOWER LEADING TO A FLATTER/NARROWER CONVECTIVE
LINE/COMPLEX ACROSS CENTRAL LA...YET THESE GUIDANCE MEMBERS ARE
MOST ALIGNED WITH RECENT EVOLUTION.  THESE GUIDANCE MEMBERS ARE
ALSO SUGGESTING AS THE MAIN PUSH OF THE COLD FRONT/HEIGHT FALLS
ADVANCE THE LOW LEVEL MOISTURE TRANSPORT WILL BECOME A BIT MORE
ALIGNED VERTICALLY WITH FLOW ALOFT INCREASING PROPAGATION VECTORS
EASTWARD WHILE REDUCING IN STRENGTH...THINNING THE LINE INTO SE LA
TOWARD 08-09Z.  EXPECTATION IS THAT WIDTH IS A BIT TOO NARROW AND
EASTWARD ADVANCEMENT MAY BE UNDERESTIMATED INCREASING THE FLOODING
THREAT EASTWARD AS WELL THOUGH EARLY MORNING...THOUGH LIKELY NOT
AS FAR EAST AS NEW ORLEANS/EAST OF I-55.  WILL CONTINUE TO MONITOR
CLOSELY.

GALLINA

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...JAN...LCH...LIX...

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

LAT...LON   31969109 31729041 29869082 29469144 29739324
            29769384 30709340 30999231



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