SPC MD 879

MD 0879 CONCERNING SEVERE POTENTIAL…WATCH LIKELY FOR FAR SERN SD…WRN IA…CNTRL/ERN NEB


MESOSCALE DISCUSSION 0879
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT WED MAY 23 2012

AREAS AFFECTED...FAR SERN SD...WRN IA...CNTRL/ERN NEB

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 231956Z - 232130Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...THUNDERSTORM DEVELOPMENT IS FORECAST TO OCCUR BY LATE
AFTERNOON ACROSS PORTIONS OF FAR SERN SD...WRN IA...AND CNTRL/ERN
NEB. LARGE HAIL AND DAMAGING WINDS WILL BE POSSIBLE. WW IS LIKELY.

DISCUSSION...MESOANALYSIS AT 19Z SHOWED A WEAK SURFACE LOW PRESSURE
CENTER LOCATED INVOF SERN SD/NWRN IA/NERN NEB...WITH A COLD FRONT
EXTENDING SWWD FROM THE LOW INTO N-CNTRL KS. SURFACE TEMPERATURES
AHEAD OF THE COLD FRONT ARE WARMING TO AROUND 90F...WITH DEWPOINTS
IN THE 50S TO NEAR 60F. GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE
RATES /NEAR 7 C PER KM IN THE 700-500 MB LAYER/...MLCAPE VALUES HAVE
INCREASED TO 1500 J/KG. SURFACE HEATING ALONG AND AHEAD OF THE FRONT
IS ALSO AIDING IN STRONG BOUNDARY LAYER DESTABILIZATION...WHICH IS
RESULTING IN THE DEVELOPMENT OF AN EXPANSIVE CUMULUS FIELD OVER
CNTRL/ERN NEB. COMBINATION OF BROAD MIDLEVEL HEIGHT FALLS AND
EMBEDDED UPPER PERTURBATIONS...AS WELL AS FRONTAL CONVERGENCE
ENHANCED WITHIN EXIT REGION OF 30-50 KT LLJ SHOULD SUPPORT
THUNDERSTORM DEVELOPMENT BY LATE AFTERNOON...WITH COVERAGE
INCREASING TOWARD NIGHT. MOST LIKELY SCENARIO IS FOR STORMS TO
REMAIN ANCHORED VERY CLOSE TO THE FRONTAL BOUNDARY...WITH ACTIVITY
POSING A THREAT FOR LARGE HAIL GIVEN THE THERMODYNAMIC ENVIRONMENT
COUPLED WITH EFFECTIVE BULK WIND DIFFERENCE VALUES FROM 30-50 KT. IN
ADDITION...UPSCALE GROWTH INTO A LINEAR SYSTEM SUGGESTS DAMAGING
WIND THREAT WILL ALSO EXIST.

..GARNER/WEISS.. 05/23/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...DMX...FSD...OAX...TOP...GID...LBF...

LAT...LON   40589956 41879853 43449617 43109488 42119479 40709587
            39909795 39989940 40589956

via SPC Forecast Products http://www.spc.noaa.gov/products/md/md0879.html