[MCD] SWOMCD

[Mesoscale Convective Discussions]

ACUS11 KWNS 201742
SWOMCD
SPC MCD 201742 
MTZ000-WYZ000-IDZ000-201945-

MESOSCALE DISCUSSION 0905
NWS STORM PREDICTION CENTER NORMAN OK
1242 PM CDT SAT MAY 20 2006

AREAS AFFECTED...SOUTHWEST/CENTRAL MT INTO NORTHERN WY

CONCERNING...SEVERE THUNDERSTORM POTENTIAL 

VALID 201742Z - 201945Z

SEVERE THREAT IS EXPECTED TO INCREASE THROUGH THE AFTERNOON ACROSS
SOUTHWEST/CENTRAL MT INTO NORTHERN WY. PRIMARY HAZARD WILL BE LARGE
HAIL...WITH DAMAGING WIND GUSTS ALSO POSSIBLE. A SEVERE THUNDERSTORM
WATCH MAY BE NEEDED IN THE NEXT 1-2 HOURS.

WATER VAPOR IMAGERY DEPICTS WELL DEFINED SHORTWAVE IMPULSE MOVING
NORTHEASTWARD ACROSS ID/WESTERN MT EARLY THIS AFTERNOON. FORCING FOR
ASCENT TIED TO THIS FEATURE...AUGMENTED BY AMPLE HEATING/LOW LEVEL
UPSLOPE COMPONENT...WILL LEAD TO INCREASING THUNDERSTORM COVERAGE
THROUGH MID/LATE AFTERNOON FROM SOUTHWEST MT INTO CENTRAL
MT/NORTHERN WY.

A VERY MOIST AIRMASS EXISTS ACROSS THE REGION...WITH SURFACE
DEWPOINTS IN THE LOWER 50S AND PW VALUES AROUND 180 PERCENT OF
NORMAL PER 12Z OBSERVED RAOBS AT GREAT FALLS MT/RIVERTON WY. AS
CONVECTIVE INHIBITION QUICKLY ERODES...MODIFIED 12Z RAOBS IN
ACCORDANCE WITH LATEST RUC SOUNDINGS IS SUPPORTIVE OF MUCAPE VALUES
OF 1500-2000 J/KG OR GREATER. COUPLED WITH MODERATE
INSTABILITY/STEEP LAPSE RATES...VERTICAL SHEAR OF 35-40 KTS WILL
SUPPORT SOME SUPERCELLS AND ORGANIZED MULTICELL CLUSTERS AS STORMS
SPREAD NORTHEASTWARD WITH LARGE HAIL/DAMAGING WIND POTENTIAL.

..GUYER.. 05/20/2006

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

ATTN...WFO...BYZ...GGW...RIW...TFX...PIH...MSO...

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