MESOSCALE PRECIPITATION DISCUSSION 0642
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
237 AM EDT TUE SEP 06 2016
 
AREAS AFFECTED...SOUTHEAST SD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 060637Z - 061100Z
 
SUMMARY...STRONG MST CONVERGENCE AND LOW ANTECEDENT CONDITIONS
POSE ISOLATED FLASH FLOODING THREAT ACROSS SE SD.

DISCUSSION...HEIGHT FALLS EJECTING INTO THE CENTRAL HIGH PLAINS
HAVE SUPPORTED A SURFACE WAVE TO DEVELOP ACROSS NE CO THAT IS
ADVANCING NORTHEAST ALONG FRONTAL ZONE. STRONG 45-55 KT SWLY LLJ
EXISTS IN WARM CONVEYOR BELT AHEAD OF THE SURFACE LOW...THOUGH
DEEPENING LOW HAS SUPPORTED A BACKING OF THE LLJ ACROSS THE SAND
HILLS OF NEBRASKA ENHANCING 850-700 FRONTOGENESIS AND MOISTURE
CONVERGENCE FOR CONVECTIVE DEVELOPMENT ANAFRONTAL ALONG BOUNDARY
THAT EXTENDS ACROSS S CENTRAL SD TOWARD THE CENTRAL MN/SD BORDER. 
IR TOPS HAVE BLOSSOMED TO -68C AND RADAR MOSAIC INDICATES HVY
RAINFALL SIGNATURE WITH SOME HAIL CONTAMINATION.   HI-RES CAMS,
OBS AND LNX RADAR ESTIMATES SUGGEST RATES IN EXCESS OF 1.5"/HR AND
RAINFALL TOTALS OVER 2" WITH SOME 3" TOTALS POSSIBLE GIVEN SLOWER
CELL MOTIONS AND PROPAGATION VECTORS IN THE 10 KT RANGE COUNTER TO
THE MEAN CELL MOTION (GIVEN STRENGTH OF INFLOW LLJ).  LOW FFG
VALUES IN BELOW 2" ACROSS SE SD ALONG WITH SATURATED SOILS FROM
LAST EVENING'S RAINFALL SHOW SOME INDICATION THAT FLASH FLOODING
MAY OCCUR IN ISOLATED LOCATIONS...PARTICULARLY AT THE NORTHEAST
APEX OF THE 850MB LOW WHERE MST FLUX SHOULD STEADILY INCREASE
RAINFALL EFFICIENCY AS TPWS INCREASE TO 1.75-2".  LIMITING FACTOR
IS ON DURATION AS MID-LEVEL INSTABILITY IS LIMITED AND CONVECTION
HAS THE POTENTIAL TO EXHAUST THE 1000-1500 J/KG MUCAPES AND REDUCE
CONVECTIVE VIGOR OF UPDRAFTS AS THE LLJ SLACKENS (VEERS) BY 10-11Z.

GALLINA

ATTN...WFO...ABR...FSD...UNR...

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

LAT...LON   44849698 44239640 43299687 43079815 43079949 
            43170001 43809979 44459824