SPC AC 140727

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0227 AM CDT Wed Jun 14 2017

   Valid 161200Z - 171200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE MID
   AND LOWER MISSOURI VALLEY AND SURROUNDING PORTIONS OF THE CENTRAL
   PLAINS AND MIDDLE MISSISSIPPI VALLEY...

   ...SUMMARY...
   Thunderstorms may impact the mid and lower Missouri Valley, and
   adjacent areas of the interior U.S., Friday through Friday night,
   accompanied by at least some risk for severe weather.

   ...Discussion...
   Some expansion of general mid-level ridging appears possible across
   the subtropical eastern Pacific and northern Mexico into the
   southwestern states during this period, with ridging also building
   northward within the mid-latitude westerlies, to the west of the
   Pacific Northwest coast.  Downstream, models suggest that the
   westerlies will trend broadly cyclonic and west northwesterly across
   the northern intermountain region, Rockies and Plains, into the
   upper Mississippi Valley.  A significant short wave impulse within
   this regime may progress across the northern intermountain region
   and Rockies into the Plains by the end of the period, but this may
   be preceded by a couple of less prominent impulses across parts of
   the northern Plains and upper Mississippi Valley region Friday into
   Friday night.

   Along the southern fringe of the westerlies, the northern periphery
   of a plume of very warm elevated mixed layer air may initially surge
   northward into the mid and lower Missouri Valley region during the
   day Friday.  This appears likely to coincide with a northward return
   of seasonably moist low-level air, which models suggest will
   contribute to a sizable area of moderate to strong potential
   instability.
    
   Given this environment, vigorous thunderstorm development, including
   discrete supercells and evolving/organizing thunderstorm clusters
   appear at least possible throughout the period.  An initial
   perturbation may be supporting thunderstorm activity at the outset
   of the period across parts of the mid Missouri Valley into the Upper
   Midwest.  The details of subsequent boundary layer destabilization
   to the east/south and west may hinge on the convective evolution
   across the central Plains Thursday night, which remains uncertain at
   this time.  However, an upstream impulse may also eventually
   contribute to forcing for new thunderstorm development across the
   mid into lower Missouri Valley region late Friday afternoon and
   evening, generally within stronger lower/mid tropospheric warm
   advection on the nose of the capping elevated mixed layer air.

   The latter activity, coinciding with peak diurnal destabilization
   seems to have the greatest potential for considerable upscale growth
   and associated severe weather potential.  However, uncertainties for
   even this development (largely due to sub-synoptic scale
   developments) still seem too large to outlook more than 5 percent
   severe probabilities at this time.

   ..Kerr.. 06/14/2017

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