SPC AC 281954

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0254 PM CDT Sun May 28 2017

   Valid 282000Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF TX
   INTO FAR WESTERN LA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   IN/MI/OH INTO NC...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF TX
   TO THE NORTHERN GULF COAST...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE GREAT
   LAKES AND OH VALLEY TO THE CAROLINAS...

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

   ...SUMMARY...
   Severe thunderstorms capable of large hail and damaging winds will
   be possible this afternoon and tonight over portions of
   southern/central Texas northeastward into Louisiana.  Other severe
   storms may occur over parts of the upper Ohio Valley, central
   Appalachians, and Carolinas.

   ...20z Update...

   Minor adjustments have been made to the slight risk area across
   Louisiana and the marginal risk further east across the Deep South.
   This is based on latest observations indicating outflow from
   convection, now located near the Gulf Coast, has resulted in weaker
   instability and capping further north. Additionally, hi-res guidance
   suggests the greatest threat into the overnight hours will reside
   mainly across TX into far western LA. Here, severe thunderstorms are
   expected to develop from late this afternoon into tonight along a
   weak surface boundary aligned with a corridor of extreme
   instability. Hail and damaging gusts will be the main concern into
   tonight.

   Other minor modifications were made to the marginal risk across the
   Great Lakes based on trends in hi-res guidance and lack of greater
   destabilization ahead of the approaching shortwave trough.

   ..Leitman.. 05/28/2017

   .PREV DISCUSSION... /ISSUED 1058 AM CDT Sun May 28 2017/

   ...TX/LA...
   After a very convectively active Saturday, the reservoir of extreme
   CAPE values is now restricted to portions of TX/LA.  Dewpoints in
   the 70s and strong daytime heating will yield a corridor of 4000+
   J/kg CAPE by mid/late afternoon across central and northeast TX,
   into western LA.  12z model solutions are consistent in the
   development of scattered thunderstorms along this corridor - mainly
   focused along a weak surface boundary evident in observations and
   satellite imagery.  Low-level shear is rather weak in this area, and
   deep-layer effective shear is marginal for supercell structures. 
   Nevertheless, slow-moving severe multicell to occasional supercell
   storms are expected with a risk of large hail and damaging winds. 
   This threat will last through most of the evening hours.

   ...IN/OH/Lower MI...
   A progressive mid-level shortwave trough is currently moving
   eastward across WI, and will affect the central Great Lakes region
   later today.  Scattered thunderstorms are forecast to develop from
   western Lower MI into northern IN by mid afternoon, with other
   storms building eastward along a weak warm front into northern OH. 
   CAPE/shear combinations are not particularly strong in this region,
   but cool temperatures aloft and the approaching shortwave trough may
   be sufficient for a few severe storms capable of hail and damaging
   winds.  The activity may develop eastward into western PA and
   northern WV before weakening.

   ...VA/NC...
   Visible satellite imagery shows strong heating is occurring over
   much of NC and south-central VA this morning.  Ample low level
   moisture remains in place across this area, leading to a moderately
   unstable air mass later today.  Scattered thunderstorms are expected
   to develop during the max heating period, with a few of the storms
   posing a risk of damaging wind gusts and perhaps hail.

   ...WY/SD/NE...
   Scattered thunderstorms will develop later this afternoon and early
   evening within a northwest flow regime over the Black Hills and
   surrounding region.  Steep mid-level lapse rates and sufficient CAPE
   suggest some risk of hail and gusty winds in the stronger cells.

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