SPC AC 140730

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0230 AM CDT Fri Jul 14 2017

   Valid 161200Z - 171200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE OHIO VALLEY/GREAT LAKES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHERN ROCKIES AND NORTHERN PLAINS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur across parts of
   the Ohio Valley and Great Lakes region in addition to the northern
   Rockies and northern Plains.

   ...Ohio Valley/Great Lakes...
   An upper low is likely to continue southeastward across the region
   on Sunday, with a cold front also progressing southeastward. The
   strongest diurnal destabilization is currently expected from parts
   of OH/IN westward into IL, although overall forcing/mass convergence
   is expected to be weaker along the front with westward extent.
   Uncertainties also exist regarding the extensiveness and impacts of
   prior-day convection upstream Saturday afternoon/night. Regardless,
   given a moist pre-frontal environment and the possibility of
   moderate quantities of buoyancy and effective shear, at least some
   potential will exist across the region for damaging winds and
   possibly some hail.

   ...Northern Rockies to Dakotas...
   An upper trough likely to be over the Canadian Rockies early Sunday
   will continue eastward toward the Canadian prairies, with height
   falls overspreading MT/northern WY into the Dakotas through Sunday
   afternoon and night. Only modest moisture will precede an
   east/southeastward-spreading surface low and front, although
   post-frontal moistening should occur late in the day across southern
   MT and northern WY. While deep-layer shear will also be relatively
   weak (25-30 kt or less), steep lapse rates related to a relatively
   hot/well-mixed boundary layer could support some potential for
   severe-caliber downdrafts with any thunderstorms that develop over
   the higher terrain and mountains of ID/southern MT/northern WY
   and/or along and just behind the advancing front/triple point
   extending into the Dakotas.

   ...Southeast states...
   A few strong to locally severe pulse-type thunderstorms could occur
   Sunday afternoon into early evening within a moist environment along
   and south of a stalled and weakening front. While a few severe
   storms could occur, the specific locations and likelihood of such is
   questionable given overall weak/subtle forcing mechanisms and
   uncertain impacts of prior-day convection.

   ...AZ/Desert Southwest...
   A few strong storms could occur Sunday afternoon and evening as a
   moist monsoon-related air mass persists across the region. However,
   with expectations of modestly weakening ridge into Sunday, steering
   winds off the high terrain should be weaker than prior days.

   ..Guyer.. 07/14/2017

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