MESO: Mesoscale Discussion 0805

ACUS11 KWNS 122255
SWOMCD
SPC MCD 122254
SDZ000-NDZ000-130030-

MESOSCALE DISCUSSION 0805
NWS STORM PREDICTION CENTER NORMAN OK
0554 PM CDT TUE MAY 12 2009

AREAS AFFECTED...THE DAKOTAS

CONCERNING...SEVERE THUNDERSTORM WATCH 289...

VALID 122254Z - 130030Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 289
CONTINUES.

ADDITIONAL CENTRAL SOUTH DAKOTA COUNTIES MAY NEED TO BE LOCALLY
ADDED TO WATCH WITHIN THE NEXT HOUR OR SO

A SMALL BUT PROMINENT EASTWARD ACCELERATING STORM CLUSTER HAS
EVOLVED OUT OF A PRE-FRONTAL HIGH PLAINS SUPERCELL. THIS APPEARS TO
BE AIDED BY STRONG AND FOCUSED FORCING IN THE EXIT REGION OF A 50-70
KT WESTERLY 500 MB JET STREAK EMANATING FROM THE NORTHERN
INTERMOUNTAIN REGION. THIS FORCING...COUPLED WITH WARM ADVECTION ON
THE NOSE OF A LOWER/MID TROPOSPHERIC THERMAL RIDGE ACROSS THE
PLAINS...IS EXPECTED TO SUSTAIN CONVECTIVE DEVELOPMENT ACROSS
NORTHERN SOUTH DAKOTA AND SOUTHERN NORTH DAKOTA WELL INTO THE
EVENING HOURS. LOW-LEVEL AMBIENT FLOW IS WEAK...BUT WITH AN
EASTERLY COMPONENT SYSTEM RELATIVE INFLOW MAY BE AS STRONG AS 50-60
KT...WHICH COULD AID THE EVOLUTION OF AN EXPANDING AND INCREASINGLY
ORGANIZED MESOSCALE CONVECTIVE SYSTEM...AS ACTIVITY ADVANCES INTO AN
INCREASINGLY MOIST LOW-LEVEL ENVIRONMENT DEEPER INTO THE PLAINS.
LARGE HAIL MAY ACCOMPANY STRONGER CELLS...BUT THE PRIMARY SEVERE
THREAT MAY BE VERY STRONG/DAMAGING SURFACE GUSTS WHICH COULD IMPACT
BISMARCK/MOBRIDGE...PERHAPS PIERRE BY/SHORTLY AFTER 01Z.

..KERR.. 05/12/2009

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

ATTN...WFO...ABR...BIS...UNR...

LAT...LON 45940224 46720185 47310108 47450056 46759950 45949952
45089963 44549973 44310023 44460087 44530153 45030224
45940224

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