SPC AC 191253

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0753 AM CDT Fri May 19 2017

   Valid 191300Z - 201200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS NORTH
   TEXAS AND SOUTHERN OKLAHOMA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
   PLAINS TO THE OHIO VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   SOUTHERN PLAINS TO THE MID-ATLANTIC STATES...

   ...SUMMARY...
   Severe thunderstorms will be possible across parts of the southern
   Plains northeastward into the Ozarks and Ohio Valley mainly this
   afternoon and evening.

   ...Synopsis...
   Within the southern stream of split westerlies over the CONUS and
   Canada, a closed upper trough centered over the central and southern
   Rockies early this morning will continue slowly northeastward,
   reaching the central High Plains by early Saturday.  

   ...Southern Plains to Ozarks...
   The extensiveness of Thursday night's storms and related convective
   overturning across parts of the region, along with additional
   ongoing early-morning development, complicate the forecast scenario.
   These factors cast some uncertainty regarding the location of peak
   severe risk later today ahead of an east/southeastward-moving cold
   front. 

   Strong to severe thunderstorms have been common through the
   overnight within a corridor across the Low Rolling Plains of
   west-central TX into western parts of north TX. These storms may
   continue to grow upscale early today and persist east/northeastward
   across north-central with some severe risk continuing, although the
   low-level jet and related inflow should diurnally weaken. Multiple
   storm-scale scenarios are plausible including diurnal eastward
   persistence within a destabilizing air mass and/or a gradual morning
   decay with subsequent redevelopment this afternoon across
   north-central TX and south-central/southeast OK along eastern
   peripheral outflow. Either scenario seems to suggest that a
   semi-focused severe corridor is most evident across north-central TX
   into parts of southern OK.

   Farther north/northeast, details are a bit more uncertain from other
   parts of OK into KS and the Ozarks region, especially considering
   convectively overturned areas spanning northeast OK into MO into
   northern AR (reference stability of 12Z SGF observed sounding) and
   ongoing thunderstorm clusters across north TX. Nonetheless, at least
   a modest degree of gradual air mass recovery/re-moistening and
   destabilization is expected ahead of the east/southeastward-moving
   cold front. Strengthening but somewhat backing (especially later
   this afternoon) mid-level southwesterly winds will support some
   initial supercells capable of hail. At least some damaging wind risk
   and tornado risk should evolve by late afternoon into evening as
   low/mid-level winds increase and as storms cluster and grow upscale
   within a corridor across eastern OK/southeast KS into AR and
   southern MO. Spatial adjustments to the Enhanced Risk could be
   warranted later today pending reassessments of the diurnal degree of
   destabilization.

   ...Ohio Valley to central Appalachians and mid-Atlantic States...
   An MCV continues to influence an east/northeastward-moving MCS
   across downstate IL during the predawn hours. While the
   wind-producing MCS should weaken this morning, renewed thunderstorm
   intensification seems viable across the downstream lower/middle Ohio
   River Valley as the MCV interacts with a southward-sagging front.
   Strengthening mid-level westerlies atop the frontal zone combined
   with steepening low-level lapse rates and moderate buoyancy south of
   the front will support intensifying eastward-moving storm clusters
   through the afternoon into evening. This includes parts of KY and
   southern IN/OH eastward to the central Appalachians and downstream
   mid-Atlantic region. Damaging winds gusts will be the primary risk
   aside from some marginally severe hail.

   ..Guyer/Jewell.. 05/19/2017

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