Severe Storm Outlook Narrative (AC)
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000
ACUS11 KWNS 262022
SWOMCD
SPC MCD 262021
NDZ000-MTZ000-WYZ000-IDZ000-262215-

Mesoscale Discussion 0532
NWS Storm Prediction Center Norman OK
0321 PM CDT Sat May 26 2018

Areas affected...Portions of Montana and far northwest Wyoming

Concerning...Severe potential...Watch possible

Valid 262021Z - 262215Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms are expected to increase in
coverage/intensity this afternoon and evening with severe wind/hail
possible. Trends will be monitored for a possible WW issuance.

DISCUSSION...Visible satellite and radar imagery from 2015Z shows
thunderstorms starting to form over the higher terrain of southwest
Montana and northwest Wyoming. RAP analysis suggests moderate
instability over the area (e.g., MLCAPE 1000-2500 J/kg), as strong
insolation (e.g., temperatures in the 70s and 80s) has occurred
within an environment characterized by surface dew points generally
in the 50s and steep mid-level lapse rates. Effective bulk shear
values of 25-35 knots suggest that if storms are able to move off
the higher terrain then they would pose a severe hail/wind threat as
they exhibit transient supercell characteristics (i.e., mid-level
rotation).

Visible satellite imagery and RAP mesoanalysis suggest that a
capping inversion currently resides across portions of
central/eastern Montana. CAM guidance continues to insist that the
CAP will erode enough for at least isolated storm formation around
22-23Z. Large hail and severe wind gusts will be possible with this
activity as it spreads eastward toward North Dakota through the
evening.

A WW issuance may be needed if storms can move off the higher
terrain and/or storms are able to form over portions of
central/eastern Montana.

..Elliott/Hart.. 05/26/2018

...Please see www.spc.noaa.gov for graphic product...

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

LAT...LON   44050901 44471028 44571082 44801193 44941255 44981296
            45421327 46071342 46481344 47111283 47431152 48490873
            48990800 48990396 46620395 45530551 44650818 44050901




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