MESOSCALE PRECIPITATION DISCUSSION 0024
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
423 PM EST WED FEB 21 2018

AREAS AFFECTED...FAR SERN TX INTO CNTRL/NRN LA AND W-CNTRL MS

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

VALID 212121Z - 220200Z

SUMMARY...FLASH FLOODING SHOULD LIKELY CONTINUE FROM PORTIONS OF
FAR SERN TX INTO CNTRL/NRN LA AND W-CNTRL MS INTO THE EARLY
EVENING HOURS. AN ADDITIONAL 2-4 INCHES WILL BE POSSIBLE ON TOP OF
EARLIER HEAVY RAINFALL FROM LATE THIS MORNING/EARLY AFTERNOON.

DISCUSSION...OBSERVATIONAL TRENDS OVER THE PAST FEW HOURS HAVE
SHOWN THE HEAVIEST RAINFALL RATES...EXCEEDING 3 IN/HR
LOCALLY...WITH AN MCV PROPAGATING NEWD ALONG A SLOW MOVING FRONT
IN LA. THE MCV WAS LOCATED ALONG THE NRN LA/MS BORDER NEAR I-20 AS
OF 2100Z...BUT IT HAS WEAKENED FROM EARLIER GIVEN WARMING CLOUD
TOPS ON GOES 16 10.3 MICRON IMAGERY AND LOWERING DUAL-POL RAINFALL
RATES INTO THE 1-2 IN/HR RANGE. HOWEVER...MLCAPE NEAR 500 J/KG IS
STILL IN PLACE ALONG AND JUST SOUTH OF THE QUASI-STATIONARY FRONT
EXTENDING INTO NRN MS WHICH MAY CONTINUE TO SUPPORT RAINFALL RATES
OF 1-2 IN/HR IN THE SHORT TERM AS THE MESO-LOW CONTINUES TO TRACK
ALONG THE FRONT INTO NRN MS THROUGH 00Z. LOCALIZED TRAINING WITH
THESE RATES WOULD GET NEAR FLASH FLOOD GUIDANCE OF 2-3 INCHES IN 3
HOURS ACROSS NRN MS.

FARTHER SOUTH...AN INFERRED SLOW MOVING SURFACE WAVE LOCATED IN
FAR EAST TEXAS ALONG THE FRONT AT 21Z IS NOT FORECAST TO MOVE MUCH
OVER THE NEXT FEW HOURS. WHILE LOW LEVEL CONFLUENCE HAS DECREASED
ACROSS CNTRL LA WHEN COMPARED TO EARLIER THIS AFTERNOON...THE
CONTINUED INFLUX OF PRECIPITABLE WATER VALUES BETWEEN 1.50 AND
1.75 INCHES WILL CONTINUE TO SUPPORT RAINFALL RATES OF 1 TO 2+
IN/HR WHERE IDEAL TRAINING DEVELOPS GIVEN CONTINUED UNIDIRECTIONAL
FLOW NEARLY PARALLEL TO THE SURFACE FRONT AND LINGERING...ALBEIT
WEAKENING...INSTABILITY. THE GREATEST POTENTIAL FOR TRAINING WILL
BE NEAR THE STRONGEST 850 MB WIND SPEEDS...30-40+ KT...FORECAST TO
REMAIN FROM THE TX/LA BORDER TO THE NRN LA/MS BORDER IN THE SHORT
TERM...WEAKENING FROM WEST TO EAST AS AN UPPER LEVEL SHORTWAVE
OVER WEST TX CONTINUES TO ADVANCE EAST.

ADDITIONAL RAINFALL ON TOP OF AN ESTIMATED 3-5 INCH BROKEN SWATH
OF EARLIER RAINS FROM FAR SERN TX INTO CNTRL/NRN LA WILL CONTINUE
ONGOING FLASH FLOODING ACROSS THE REGION.

OTTO

ATTN...WFO...HGX...JAN...LCH...MEG...SHV...

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

LAT...LON   34638905 34508851 34158842 33648874 32619008
            31639153 31309218 31069281 30719357 30279477
            31099502 32269389 32649261 33119145 33849050
            34408986