SPC AC 191256

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0756 AM CDT Sat May 19 2018

   Valid 191300Z - 201200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
   KANSAS AND FAR SOUTHEAST NEBRASKA INTO MISSOURI AS WELL AS WESTERN
   OKLAHOMA AND WESTERN NORTH TEXAS...

   ...SUMMARY...
   Severe thunderstorms will develop across the central and southern
   Plains into the lower Missouri Valley Saturday. Very large hail and
   damaging winds are the primary threats. A few strong storms are also
   possible from eastern Ohio and Kentucky into western Pennsylvania
   and West Virginia.

   ...Central and Southern Plains to the Lower Missouri/middle
   Mississippi Valleys...
   Extensive convection across Kansas early in the overnight has
   gradually diminished and become more scattered in coverage through
   the early morning hours, although storms have continued to
   regenerate especially across southeast Kansas into southwest
   Missouri amidst an elevated moisture transport regime. Reference
   Mesoscale Discussion 459 regarding this early-day activity. Related
   cloud cover and convective overturning somewhat complicates the
   forecast details, although appreciable air mass recovery across
   Kansas into nearby Nebraska and Missouri is plausible by peak
   heating, particularly given a reservoir of unperturbed theta-e
   across Oklahoma.

   On the east-southeast periphery of a weak/slow-moving upper low over
   the central High Plains, a ribbon of moderately strong southwesterly
   winds will overspread a southwest/northeast-oriented frontal zone,
   which has been convectively modified in areas. Although the
   persistence of early-day storms and the impacts/disposition of
   outflows are points of uncertainty, current thinking is that
   surface-based storms are most likely to develop this afternoon
   across east-central/northeast Kansas near a triple point, with the
   northern extent (such as southeast Nebraska and southern Iowa) of
   the surface-based severe risk complicated by lingering cloud cover
   and a southward-advancing secondary front.

   Regardless, deep-layer/low-level shear are expected to be maximized
   in this general vicinity with the potential for initial supercells
   capable of large hail and at least some tornado risk. These
   initially more discrete storms should merge and grow upscale early
   this evening as they spread toward western/northern Missouri. A
   semi-focused corridor of damaging winds, and possibly a few
   QLCS-related tornadoes, may evolve across western and northern of
   Missouri this evening.

   Farther southwest, other surface-based severe storms are expected to
   develop as early as mid-afternoon along the southwestward-extending
   front across western Oklahoma and western parts of north Texas and
   in vicinity of a dry line across west Texas. Steep lapse rates and
   season-typical moisture content will support upwards of 2500-3500
   J/kg MLCAPE by peak heating. Mid-level southwesterly winds will be
   maximized across western Oklahoma and nearby north/northwest Texas
   with as much as 35-40 kt of effective shear. This will support
   initial supercells capable of large hail. In the presence of
   relatively weak boundary layer winds and somewhat high cloud bases,
   storms should cluster and congeal through early/mid-evening as steep
   lapse rates and ample dry air above the boundary layer promote
   strong downdrafts and the potential for severe-caliber wind gusts,
   particularly across parts of western Oklahoma and the Low Rolling
   Plains of north Texas. Other, somewhat more isolated, severe storms
   capable of large hail are expected as far south as the Texas Big
   Bend vicinity.

   ...Ohio Valley to the north-central Appalachians...
   Modestly enhanced low/mid-level winds are expected across the region
   to the east of an gradually weakening upstream shortwave trough.
   Generally moist profiles are anticipated with the resulting modest
   instability and weak mid-level lapse rates precluding robust
   updrafts. Even so, a few bowing segments/stronger downdrafts capable
   of locally damaging wind gusts are possible.

   ..Guyer/Goss.. 05/19/2018

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