SPC MD 675

MD 0675 CONCERNING SEVERE POTENTIAL…WATCH LIKELY FOR NWRN KS…NERN CO AND WRN NEB


MESOSCALE DISCUSSION 0675
NWS STORM PREDICTION CENTER NORMAN OK
0209 PM CDT SAT MAY 18 2013

AREAS AFFECTED...NWRN KS...NERN CO AND WRN NEB

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 181909Z - 182045Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...STORMS ARE EXPECTED TO INITIATE BY 20-21Z FROM NERN CO
INTO NWRN KS AND EXTREME SERN WY...THEN SUBSEQUENTLY DEVELOP NEWD
INTO WRN NEB DURING THE EVENING. PRIMARY THREATS WILL BE VERY LARGE
HAIL AND ISOLATED TORNADOES. STORMS MAY EVENTUALLY GROW UPSCALE INTO
ONE OR MORE CLUSTERS LATER IN THE EVENING WITH AN INCREASING THREAT
FOR DAMAGING WIND. A TORNADO WATCH WILL LIKELY BE NEEDED PRIOR TO
21Z.

DISCUSSION...THIS AFTERNOON A DRYLINE EXTENDS FROM SERN WY TO A
MESOLOW NEAR THE KS/CO BORDER THEN FARTHER SWD THROUGH SWRN KS. THE
LATEST OBJECTIVE ANALYSIS INDICATES THE WARM SECTOR HAS BECOME VERY
UNSTABLE IN CORRIDOR FROM NWRN KS THROUGH EXTREME NERN CO AND WRN
NEB WHERE VERY STEEP LAPSE RATES /APPROACHING 9 C/KM/ HAVE
OVERSPREAD THE MOIST AXIS. SPECIAL 18Z RAOB FROM NORTH PLATTE NEB
INDICATES A STRONG CAPPING INVERSION IS STILL IN PLACE JUST BELOW
700 MB IN ASSOCIATION WITH WARM AIR AT BASE OF THE EML. THIS
SUGGESTS THUNDERSTORM INITIATION WILL LIKELY BE FARTHER WEST ACROSS
NERN CO AND NWRN KS. SATELLITE IMAGERY SHOWS MID-LEVEL CONVECTION
SPREADING RAPIDLY NWD ACROSS NERN CO AND NWRN KS AND APPEARS TO BE
IN ASSOCIATION WITH MID-LEVEL ASCENT ACCOMPANYING A NEWD EJECTING
SHORTWAVE TROUGH. FORCING FROM THIS FEATURE AND DEEPER MIXING OVER
THE HIGH PLAINS OF NERN CO THROUGH WRN KS WILL LIKELY SUPPORT
THUNDERSTORM INITIATION ALONG THE DRYLINE SOMETIME DURING THE NEXT
COUPLE HOURS.

VERTICAL SHEAR THROUGH A DEEP LAYER WILL REMAIN SUFFICIENT FOR
SUPERCELLS CAPABLE OF VERY LARGE HAIL GIVEN THE FAVORABLE LAPSE
RATES AND STRONG INSTABILITY. ALSO...THE THREAT FOR ISOLATED
TORNADOES IS EXPECTED TO INCREASE IN WINDOW FROM LATE AFTERNOON INTO
EARLY EVENING AS THE LLJ STRENGTHENS AND BEFORE THE BOUNDARY LAYER
DECOUPLES AND WHILE SOME STORMS MAY STILL BE DISCRETE. STORMS MAY
EVENTUALLY CONGEAL INTO ONE OR MORE CLUSTERS DURING THE
EVENING...WITH AN ATTENDANT INCREASE IN DAMAGING WIND THREAT.

..DIAL/KERR.. 05/18/2013

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

ATTN...WFO...GID...LBF...GLD...BOU...CYS...

LAT...LON   39030147 39950243 40740317 42060386 42720319 42270080
            39630003 38840064 39030147

via SPC Forecast Products http://www.spc.noaa.gov/products/md/md0675.html