SPC AC 110557

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CDT Fri May 11 2018

   Valid 111200Z - 121200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   SOUTHEAST WYOMING AND ADJACENT NORTHEAST COLORADO AND SOUTHWEST
   PARTS OF THE NEBRASKA PANHANDLE...

   ...SUMMARY...
   Isolated thunderstorms with accompanying large hail and wind
   potential will be possible across parts of the central High Plains
   this afternoon and evening.  A stronger/marginally severe storm or
   two may also occur over a portion of the southern High Plains
   vicinity, and across the upper Ohio Valley area.

   ...Synopsis...
   Fast west-northwesterly flow aloft will prevail across the Midwest
   and Northeast, north of a southeast U.S. ridge and east of a large
   upper trough evolving over the western states.  Within the broader
   cyclonic flow, a closed low is forecast to dig southward into the
   Great Basin through the period.

   At the surface, a wavy frontal zone should extend from the central
   High Plains across Kansas and northern Missouri into/across the
   Midwest, while a cold front crosses the Great Basin and vicinity. 
   Elsewhere, high pressure will prevail over the Southeast.

   ...Southeast Wyoming into parts of northeast Colorado and adjacent
   parts of the Nebraska Panhandle...
   Easterly upslope flow to the cool side of the surface boundary in
   conjunction with modest destabilization should support development
   of isolated thunderstorms -- perhaps as far west as south-central
   Wyoming nearer the eastern fringe of the upper low.  Flow veering
   with height to southwesterly at mid levels will yield shear
   sufficient for organized storms, and thus a few of the
   stronger/rotating cells will likely pose a risk for locally damaging
   winds and/or hail.  Risk should remain confined to the High Plains,
   as an increasingly capped airmass with eastward extent should prove
   hostile for migration of convection off the higher terrain. 

   ...Eastern portions of the Texas and Oklahoma Panhandles into parts
   of southwest Kansas and western Oklahoma...
   Deep diurnal mixing near the dryline, and a moderately unstable
   airmass farther east, may support development of a couple of
   thunderstorms over eastern portions of the Texas and Oklahoma
   Panhandles/southwest Kansas vicinity by late afternoon.  Capping
   should prohibit more widespread convective development, but
   potential for wind damage associated with evaporatively aided gusts
   appears sufficient to maintain a small MRGL risk area.  Convection
   should rapidly diminish after sunset, as the boundary layer
   stabilizes and the capping inversion becomes re-established.

   ...The upper Ohio Valley vicinity...
   As a weak/fast-moving short-wave trough crosses the Midwest, diurnal
   heating will contribute to moderate destabilization along the
   surface frontal zone progged to lie across the upper Ohio Valley
   area.  Weak ascent associated with the short-wave feature -- focused
   in the vicinity of the front -- may support development of isolated
   storms during the late afternoon and early evening hours.  With
   strengthening/weakly veering flow with height providing ample shear,
   one or two of these storms may reach severe levels, with attendant
   risk for a locally damaging gust or two, and possibly marginal hail.
   Storms should diminish gradually through the evening as they shift
   across western Pennsylvania and into the mountains.

   ..Goss.. 05/11/2018

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