SPC AC 111731

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1231 PM CDT Thu May 11 2017

   Valid 121200Z - 131200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHEAST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   WESTERN AND CENTRAL MONTANA...

   ...SUMMARY...
   Strong storms are possible across portions of the Deep South to the
   southern Appalachians, as well as across parts of west-central
   Montana on Friday.  Gusty winds and hail are the main concerns with
   these storms.

   ...Synopsis...
   While a large/deep upper low just off the western Canada/Pacific
   Northwest coast early Friday moves slowly inland, cyclonic flow
   surrounding a second low -- over western Ontario -- is forecast to
   expand southeastward across the Great Lakes region during the
   period.  Meanwhile, an eastward-moving short-wave trough, south of
   aforementioned/southward-expanding northern stream cyclonic flow
   field, is progged to shift eastward across the southeast quarter of
   the U.S. through the period.

   At the surface, a weak cold front is forecast to advance southeast
   across the southeast states in conjunction with the eastward-moving
   mid-level wave, while in the West a cold front associated with the
   inland-moving upper system will cross the Intermountain West through
   the period.

   ...The Southeast...
   Showers and embedded thunderstorms should be ongoing at the start of
   the period to the northwest of the risk area, in the vicinity of the
   southeastward-moving cold front.  While clouds and ongoing
   precipitation may hinder destabilization across portions of the
   area, a moist boundary layer and some heating should yield
   mixed-layer CAPE generally in the 1000 to 1500 J/kg range.  A
   gradual increase in storms is expected through the afternoon, from
   portions of the Carolinas west-southwestward to the Louisiana
   vicinity, with some linear and/or multicell organization expected
   locally -- aided by moderate westerly/west-southwesterly flow at mid
   levels.  Locally gusty/damaging winds and marginally severe hail
   will be possible with the strongest convection, though
   anticipated/overall risk does not appear to warrant upgrade to 15%
   coverage/SLGT risk at this time.

   ...Western/central Montana vicinity...
   Ascent associated with the eastward advance of upper troughing and
   an associated surface cold front will support afternoon storm
   develop over western/central Montana, as some high-based CAPE
   development occurs in conjunction with daytime heating.  With amply
   strong/roughly unidirectional southerly flow aloft expected across
   the region sufficient to support organized/fast-moving storms, some
   risk for locally damaging, evaporatively enhanced gusts will be
   possible.  Risk should diminish by late evening as the lower
   troposphere cools/stabilizes.

   ..Goss.. 05/11/2017

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