SPC MD 1455

MD 1455 CONCERNING SEVERE THUNDERSTORM WATCH 427… FOR WRN/CNTRL SD…ERN WY…NERN CO…NWRN HALF OF NEB


MESOSCALE DISCUSSION 1455
NWS STORM PREDICTION CENTER NORMAN OK
0823 PM CDT SAT JUL 20 2013

AREAS AFFECTED...WRN/CNTRL SD...ERN WY...NERN CO...NWRN HALF OF NEB

CONCERNING...SEVERE THUNDERSTORM WATCH 427...

VALID 210123Z - 210300Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 427
CONTINUES.

SUMMARY...THE SEVERE THREAT CONTINUES IN AND NEAR WW 427. A SLOW
DOWNWARD TREND IN INTENSITY IS EXPECTED WITH TIME LATER THIS
EVENING. WHILE LOCAL AREAL EXPANSIONS OF THE WATCH MAY BE
NECESSARY...ADDITIONAL DOWNSTREAM WW ISSUANCE APPEARS UNLIKELY AT
THIS TIME.

DISCUSSION...NUMEROUS STRONG/SEVERE STORMS ARE ONGOING ACROSS WW 427
AS OF 0115Z. THUS FAR...THE CONVECTIVE MODE HAS MAINLY BEEN
CELLULAR...BUT STORMS HAVE RECENTLY TENDED TO CONSOLIDATE ACROSS
NWRN NEB AND NERN CO...WITH MORE ISOLATED CELLS STILL DOMINANT
ACROSS WRN SD. EFFECTIVE SHEAR OF 40-50 KTS IS MORE THAN SUFFICIENT
FOR ORGANIZED STORMS GIVEN STEEP MIDLEVEL LAPSE RATES AND MODERATE
MUCAPE OF 1000-2000 J/KG IN PLACE. LARGE HAIL WILL REMAIN POSSIBLE
WITH ANY SEMI-DISCRETE CELLS...WHILE THERE MAY BE A SHORT-TERM
INCREASE IN SEVERE WIND THREAT ACROSS WRN/CNTRL NEB AND NERN CO AS
UPSCALE GROWTH CONTINUES.

LATER THIS EVENING...INCREASING CINH IS EXPECTED TO LESSEN THE
SEVERE RISK. THE CONVECTIVE LINE ACROSS ERN CO MAY EVENTUALLY
PROPAGATE SEWD OUT OF THE WATCH INTO E-CNTRL CO/WRN KS...BUT
DECREASING SHEAR AND INCREASING CINH SHOULD LESSEN THE SEVERE THREAT
WITH SWD EXTENT. MEANWHILE...THE CONVECTIVE LINE OVER CHERRY CO NEB
WILL PROPAGATE TOWARD THE SERN EDGE OF THE WATCH DURING THE NEXT 1-2
HRS. LOCAL WATCH EXPANSION MAY BE NECESSARY TO COVER THE THREAT
ASSOCIATED WITH THIS LINE...BUT ADDITIONAL WW ISSUANCE INTO S-CNTRL
NEB APPEARS UNLIKELY AT THIS TIME AS CINH INCREASES. THE MORE
ISOLATED CELLS ACROSS SD WILL ALSO TEND TO WEAKEN LATER THIS EVENING
AS DIURNAL COOLING CONTINUES.

..DEAN.. 07/21/2013

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

ATTN...WFO...FSD...ABR...LBF...UNR...GLD...BOU...CYS...BYZ...

LAT...LON   39460471 40240479 42020504 43660502 44890452 45640378
            45550234 45370062 45139969 44529923 43709881 43079882
            42539879 42129904 41799941 41559985 41090079 40810146
            40450236 40070267 39420361 39200393 39460471

via SPC Forecast Products http://www.spc.noaa.gov/products/md/md1455.html