SPC AC 281731

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1231 PM CDT Sat Apr 28 2018

   Valid 291200Z - 301200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE HIGH
   PLAINS REGION...

   ...SUMMARY...
   Widely-scattered strong to locally severe storms capable hail and
   possibly gusty winds are expected across the High Plains from
   southeast Montana southward to the Big Bend of west Texas.

   ...Synopsis...
   A slowly progressive upper pattern -- featuring troughs over the
   eastern and western U.S. flanking a central U.S. ridge -- is progged
   across the U.S. on Sunday.  At the surface, a cold front will
   continue progressing across the western states ahead of the upper
   system, while a lee trough remains established over the High Plains.
    With time, the cold front will overtake northern portions of the
   lee trough, and continue progressing into the Dakotas/western
   Nebraska through the end of the period.

   ...The High Plains...
   Large-scale ascent -- focused near a surface lee trough over the
   High Plains -- will increase as mid-level heights fall ahead of the
   slowly advancing western upper trough.  This will result in
   conditions supportive for convective initiation evolving through the
   afternoon, as gradual/modest airmass destabilization occurs despite
   scant low-level moisture.

   With diurnal surface heating beneath steepening mid-level lapse
   rates supporting 1000 to 1500 J/kg high-based mixed-layer CAPE
   through peak heating, scattered showers and isolated thunderstorms
   should develop, from the northeast Wyoming/southeast Montana
   vicinity southward across the High Plains.  

   Along with modest but sufficient instability, marginal shear will
   likely be present across the region -- sufficient for
   semi-organized, possibly weakly rotating storms.  As such, potential
   for hail -- and possibly a damaging gust in a few locales -- is
   evident from the strongest high-based updrafts.  It would appear
   that the CAPE/shear combination may be maximized over the northern
   High Plains area -- i.e. northern portions of the marginal risk. 
   However, confidence with respect to coverage of severe storms
   precludes upgrade to 15%/slight risk at this time.  

   Convection will have a strong diurnal peak through late afternoon,
   diminishing through/after sunset as the boundary layer
   cools/stabilizes rapidly.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:  <2%     - None
   Wind:      5%     - Marginal
   Hail:      5%     - Marginal

   ..Goss.. 04/28/2018

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   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z