MESOSCALE PRECIPITATION DISCUSSION 0162
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
345 PM EDT SAT APR 29 2017

AREAS AFFECTED...NORTHWESTERN AR...SOUTHEASTERN MO...SOUTHERN IL

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

VALID 291945Z - 300100Z

SUMMARY...SLOW EASTWARD MARCH OF CONVECTIVE LINE WITH EMBEDDED
CELL MOTIONS NEARLY PARALLEL TO THE LINE ALLOWING FOR TRAINING AND
POTENTIAL FOR LIFE THREATENING FLASH FLOODING.

DISCUSSION...SURFACE ANALYSIS DEPICTS A SURFACE LOW ALONG THE RED
RIVER NEAR I-35 CROSSING WITH THE COLD FRONT EXITING NNE TO A
SURFACE REFLECTION OF BROAD MCV E OF COU IN MO.  CLEAR SKIES IN
ADVANCE OF THIS LINE SUPPORTED BY WEAK UPPER LOW HAS ALLOWED FOR
INCREASE OF INSTABILITY NEAR 3000 MLCAPES WITH DEEP AVAILABLE
MOISTURE WITH SFC TDS IN THE LOW 70S AND TPWS AROUND 1.75".  THIS
COMPOUNDED WITH DEEP SOUTHERLY LOW LEVEL JET IN THE 50-60 KT RANGE
SUPPORTS TREMENDOUS FLUX FOR HIGHLY EFFICIENT RAINFALL PRODUCTION
FOR THE CONVECTION THAT HAS BEEN DEVELOPING WITH HOURLY RATES OF
2-2.25"/HR LIKELY. 

DEEP HEIGHT FALLS REMAINING UPSTREAM AND SURFACE WAVE DEEPENING TO
THE SW AND MCV EXITING TOWARD THE NORTHEAST PLACES E CENTRAL/N AR
AND S CENTRAL MO IN A FAVORED ENVIRONMENT FOR VERY SLOW IF ANY
EASTWARD PROPAGATION PER RAP PROG. VECTORS.  THIS ALLOWS THE
CONVECTION THAT HAS BEEN FORMING ALONG PARALLEL INFLOW CU BANDS TO
GROW AND  WITH CELL MOTION VECTORS NEARLY NORTH-SOUTH...SUPPORTING
A TRAINING ENVIRONMENT EVEN WITH LIMITED LARGE SCALE EASTWARD
PROGRESSION OF THE COLD FRONT.   GIVEN THE BREADTH OF THE PARALLEL
LINES (CONGEALING IN PARTS)...RAINFALL TOTALS OVER 5" ARE POSSIBLE
IN COMPLEX TERRAIN OF THE OZARKS LEADING TO LIFE THREATENING FLASH
FLOODING TO OCCUR. 

FURTHER NORTH...STRONGER FLOW ALOFT/THICKNESS FIELDS SUPPORT
NORTHEASTWARD LIFTING OF THE MCV AND SLIGHTLY FASTER EASTWARD
ADVANCEMENT OF THE COLD FRONT/SQUALL LINE ACROSS SE MO INTO SW IL
WHICH SHOULD REDUCE DURATION OF HEAVIEST RATES...THOUGH
LARGE/BROAD MCS SHIELD POST-COLD FRONT WILL CONTINUE TO PRODUCE
.5-.75"/HR RATES FOR A FEW HOURS LEADING TO A LONGER
DURATION/INUNDATION FLOODING SETUP TO OCCUR ACROSS CENTRAL MO INTO
SE MO.  FLASH FLOODING WILL REMAIN LIKELY EVEN WITH FASTER HITTING
CONVECTION IN THE LINE FROM CHRISTIAN/TANEY COUNTY MO TO S IL
FRANKLIN/WILLIAMSON COUNTIES WHERE ONGOING FLOODING FROM LAST
NIGHT HAS REDUCED FFG VALUES BELOW .25"/HR

GALLINA

ATTN...WFO...LSX...LZK...MEG...PAH...SGF...TSA...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   39088993 38218864 36848960 35679096 34509219
            34039326 34929435 37179386 38479271