MESOSCALE PRECIPITATION DISCUSSION 0509
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1214 AM EDT WED SEP 23 2015
 
AREAS AFFECTED...SOUTHERN SOUTH DAKOTA...NORTHERN NEBRASKA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 230414Z - 230914Z
 
SUMMARY...LIKELY FLASH FLOODING GIVEN MODERATE RATES TO 1.5-2"/HR
WITH VERY SLOW CELL MOTIONS WITH UPSTREAM DEVELOPMENT.

DISCUSSION...LEADING SHORTWAVE FROM THE REMNANTS OF TROPICAL
DEPRESSION 16E CAN BE SEEN WELL IN WV/IR OVER SW NEB. THE
SHORTWAVE IS TRACKING SLIGHTLY NORTH TO NNW GIVEN BINARY
INTERACTION WITH STRONGER UPSTREAM SHORTWAVE ACROSS CENTRAL
COLORADO.  THIS ALLOWS FOR EXCELLENT DIVERGENCE IN THE VERY TIGHT
SHORTWAVE RIDGING EXTENDING OVER THE DISCUSSION AREA FROM 5H AND
ALOFT.  A STRENGTHENING SURFACE FRONTAL BOUNDARY BISECTING
NEBRASKA FROM SW TO NE AND A STRENGTHENING LOW LEVEL JET WITH
35-45 KT 850MB SOUTHERLY FLOW IS ANALYZED ACROSS W KS/E CO
ALLOWING STRONG ISENTROPIC ASCENT THROUGH A DECENTLY UNSTABLE
ENVIRONMENT ALOFT AS DENOTED BY 2000 J/KG MUCAPES THROUGHOUT THE
THE SAND HILLS OF N CENT NEB. WITH STRONG INFLOW...UPSTREAM ENERGY
CELL PROPAGATION AND CELL MOTIONS WILL BE WEAK AND COUNTER TO EACH
OTHER FOR THE NEXT FEW HOURS BEFORE SHIFTING NORTH WITH THE
ADVANCEMENT OF STRONGER FLOW.

MOISTURE AVAILABILITY HAS BEEN THE LIMITING FACTOR FROM THIS
STREAM...ON THE WESTERN SIDE OF RETURN RECYCLED CP AIR MASS
LIMITED TO 1.2-1.3" TPWS.  HOWEVER...MODERATE 7-5H SWLY FLOW IS
PUMPING INCREASED MOISTURE THROUGH THE MID-LEVELS PER CIRA 7-5H
LAYERED TPW LOOPS. ADDING AN ADDITIONAL .3-.5" TO THE LOWER LEVEL
FOR A POCKET OF 1.5-1.6" TPWS TO ALLOW FOR SOME INCREASED 
RAINFALL PRODUCTION OF 1.5-2"/HR...WITH 2-3 HOURS OF SLOW MOTIONS
TOTALS OF 4-6" ARE POSSIBLE.     

   

ATTN...WFO...ABR...FSD...LBF...OAX...UNR...

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

LAT...LON   44110066 44069880 43569697 42989664 42119644 
            41589756 42199879 42620080 43190116