MESOSCALE PRECIPITATION DISCUSSION 0452
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 AM EDT TUE AUG 18 2015
 
AREAS AFFECTED...EASTERN NEBRASKA...WESTERN IOWA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 180642Z - 181242Z
 
SUMMARY...INCREASING COVERAGE OF HIGHLY EFFICIENT THUNDERSTORMS TO
ORIENT E-W ALONG BOUNDARY ALLOWING FOR TRAINING/REPEAT

DISCUSSION...SYNOPTIC SETUP IDEAL FOR INCREASING FLASH FLOOD
THREAT... AS COLD FRONT BISECTS IOWA WITH WEAK 850MB
INFLECTION/TROF CURRENTLY OVER CENTRAL NEBRASKA WITH INCREASING
HEIGHT FALLS UPSTREAM TO ALLOW FOR BOUNDARY TO REMAIN RELATIVELY
STATIONARY THROUGH THE EARLY MORNING HOURS ACROSS WESTERN IOWA
BEFORE MAIN LOW/SQUALL LINE INTERSECTS THE BOUNDARY AROUND MIDDAY.
INSTABILITY IS RATHER MARGINAL ATTM IN THE 500-750 J/KG RANGE BUT
20KT LLJ INCREASING TO 35KT AND BROAD LARGE SCALE ASCENT FROM
INCREASING UVV FROM FAVORABLE INCREASING JET DYNAMICS ALOFT SHOULD
SUPPORT STRONG UPDRAFTS FOR EFFICIENT RAINFALL PRODUCTION.  GPS
AND RAP SUGGEST MAINTENANCE OF TOTAL PWATS IN THE 1.75" RANGE AND
SHOULD SUPPORT CONTINUING 1.5-2"/HR RANGE. 

UPPER LEVEL ENVIRONMENT SHOULD ALSO SUPPORT CELL MOTIONS TO BE
GENERALLY PARALLEL TO THE BOUNDARY WITH DECREASING PROPAGATION
VECTORS GIVEN APPROACHING UPSTREAM ENERGY. GIVEN THE BREADTH OF
THE CONVECTIVE ZONE SHOULD ALLOW FOR SOME TRAINING BUT NOT
NECESSARILY THE MOST INTENSE CORES...ALLOWING FOR A BROADER SWATH
OF MODERATE TOTALS BUT SOME TRACKS THAT SHOULD ALLOW FOR TOTALS IN
THE 2-4" RANGE OVER THE NEXT 6HRS.  ISOLATED HIGHER POCKETS MAY
OCCUR IF CELLS HANG/SLOW FORWARD PROGRESS BY TAKING ON
ROTATION/SUPERCELL NATURE...THOUGH THIS IS LESS LIKELY
PARTICULARLY FURTHER EAST INTO CENTRAL IOWA.

HI-RESOLUTION CONVECTION ALLOWING MODELS HAVE STRONG AGREEMENT IN
THIS SCENARIO  PARTICULARLY THE RECENT RUNS OF THE HRRR AND THE
NMMB AND ARW INCLUDING THEIR PARALLEL RUNS PAINTING A SWATH FROM
OMA TO DSM.  THE NAM-CONEST...SPCWRF AND GEM REGIONAL ALSO SUPPORT
THIS EVOLUTION BUT WERE A BIT FURTHER NORTH WITH SWATH OF HIGHEST
TOTALS.       

GALLINA

ATTN...WFO...DMX...OAX...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   42189515 42099280 41359254 40969316 40829448 
            40729659 40979725 41219721 41889705