Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 202019
SWOMCD
SPC MCD 202018
WYZ000-MTZ000-IDZ000-202245-

Mesoscale Discussion 1365
NWS Storm Prediction Center Norman OK
0318 PM CDT Thu Jul 20 2017

Areas affected...Portions of Wyoming...far southern
Montana...extreme southeast Idaho

Concerning...Severe potential...Watch unlikely

Valid 202018Z - 202245Z

Probability of Watch Issuance...20 percent

SUMMARY...Convection spreading across portions of the northern
Rockies vicinity into the early evening will have the potential to
produce isolated severe wind and hail. Present indications are that
Watch issuance is unlikely.

DISCUSSION...Convection continues to increase in coverage and
intensity from southeast ID to northwest WY and into adjacent MT,
peripheral to a mid-level speed maximum crossing the northern
Rockies. Related enhanced ascent, interacting with the northern
extent of monsoon-related moisture, is enhancing convective
coverage -- aided by diurnally enhanced orographic circulations. The
presence of 25-40 kt of effective shear associated with the speed
maximum is already supporting semi-organized convective structures,
which will continue tracking northeastward and eastward into the
evening hours. Sufficient mid-level moisture exists for high-based
convection to produce isolated severe wind gusts amid a
deep/well-mixed boundary layer -- especially where more-defined,
small bowing convective segments evolve. Steep mid-level lapse rates
could support some severe hail risk with more isolated, cellular
structures. However, the overall limited magnitude of boundary-layer
moisture and associated marginal buoyancy should limit overall
severe coverage.

..Cohen/Coniglio/Hart.. 07/20/2017

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

ATTN...WFO...BYZ...RIW...PIH...

LAT...LON   42851148 44571011 45450838 44660727 43430733 42420908
            42281071 42851148




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