SWOMCD
SPC MCD 081902
NDZ000-SDZ000-MTZ000-WYZ000-082030-
MESOSCALE DISCUSSION 1489
NWS STORM PREDICTION CENTER NORMAN OK
0202 PM CDT WED JUL 08 2009
AREAS AFFECTED...MT...ND...SD...WY
CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY
VALID 081902Z - 082030Z
AS ADVERTISED IN EARLIER OUTLOOKS AND EARLIER MESOSCALE
DISCUSSION...MORE WIDESPREAD AND DANGEROUS THUNDERSTORM DEVELOPMENT
APPEARS LIKELY ACROSS THE NRN HIGH PLAINS THIS AFTERNOON. THIS
DEVELOPMENT IS EXPECTED TO ENSUE WITHIN/BENEATH BELT OF STRONGLY
DIFFLUENT 60-100KT MID TO UPPER LEVEL FLOW. THESE POTENT LARGE-SCALE
KINEMATICS/DYNAMICS HAVE ALREADY RESULTED IN A VERY ORGANIZED AND
LONG-LIVED SUPERCELL THAT RACED NEWD ACROSS NERN MT THIS MORNING AND
WAS CROSSING INTO WRN ND AND WEAKENING ATTM.
IN THE WAKE OF THIS SLIGHTLY ELEVATED CELL...AIRMASS ACROSS MUCH OF
ERN MT AND ADJACENT AREAS OF ND/SD/WY HAS BECOME MORE UNSTABLE AND
UNCAPPED WITH DAYTIME HEATING. THIS DESTABILIZATION SHOULD
CONTRIBUTE TO RAPID AND ROBUST TSTM DEVELOPMENT WITHIN SURFACE
TROUGH AND AHEAD OF THE COLD FRONT NOW MOVING INTO THESE AREAS FROM
THE WEST. GIVEN DEEP-LAYER EFFECTIVE SHEAR ON THE ORDER OF
50KT...DISCRETE CELLS SHOULD QUICKLY ACQUIRE SUPERCELL STRUCTURE AND
POSE A THREAT OF LARGE HAIL. TORNADO POTENTIAL MAY EVOLVE WITH A
COUPLE OF THE MORE PERSISTENT UPDRAFTS NEAR THE LEE TROUGH AND
TRACKING PREFERENTIALLY ALONG OUTFLOW/FRONTAL AND DIFFERENTIAL
HEATING BOUNDARIES SITUATED ACROSS THE AREA. UPSCALE ORGANIZATION
ENHANCED BY THE APPROACH OF THE UPPER TROUGH AND SURFACE DEVELOPMENT
SHOULD...EVENTUALLY...AID IN LINEAR MCS DEVELOPMENT WITH WIDESPREAD
DAMAGING WIND POTENTIAL SPREADING EAST ACROSS THE DAKOTAS LATER
TODAY/TONIGHT.
..CARBIN.. 07/08/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...BIS...UNR...BYZ...GGW...
LAT...LON 48300542 48550399 48420200 47220186 45320247 44260323
43780366 43650520 43920571 44620567 47700566 48300542
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