SPC AC 181257

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0757 AM CDT Sat May 18 2019

   Valid 181300Z - 191200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MUCH OF NORTH
   TEXAS...ARKANSAS...SOUTHERN AND EASTERN OKLAHOMA...AND NORTHWEST
   LOUISIANA...

   ...SUMMARY...
   Severe storms are expected from Texas to southern Minnesota, with
   the greatest threat from north Texas across southeast Oklahoma into
   Arkansas and northwest Louisiana. A few tornadoes, some strong,
   widespread damaging winds and large hail are expected.

   ...Synopsis...
   An upper-level trough will move east into the Plains states today
   while becoming increasingly negatively tilted with time. A 70-80 kt
   mid-level speed max will rotate east/northeast across the OK/North
   TX region into southwest MO, while strengthening 850-mb winds
   increase to 40-50 kts towards 00Z Sunday. Surface low pressure over
   southeast SD will weaken as a new low develops over northwest
   OK/southern KS and lifts northeast into IA overnight.  A cold front
   trailing southwest from the surface low will move east across the
   central/southern Plains today, and a warm front extending east from
   the low through the OH Valley will lift northward. 

   ...Southern Plains/Arklatex into southern Ozarks...
   Primary change with this outlook is to expand tornado probabilities,
   including significant tornado probability, west across north TX in
   advance of on-going supercells with a history of strong low-level
   rotation and tornadoes.

   Strong/severe thunderstorms are in progress across portions of
   northwest/west TX at 13Z, including a mix of semi-discrete
   supercells and an evolving linear structure. Current expectations
   are for these storms to continue east/northeast through the
   afternoon across north TX, central/eastern OK, and western AR in
   tandem with large-scale forcing for ascent with the upper trough. 
   Steep mid-level lapse rates, sampled on regional 12Z soundings,
   combined with a very moist atmosphere will result in moderate/strong
   surface-based instability.  The presence of 45-55 kts of westerly
   deep-layer shear and increasing low-level shear will result in an
   environment supportive of damaging winds and a few tornadoes via
   mesocyclone and QLCS processes. Large hail will also be possible
   with any persistent updrafts. 

   ...South-central and Southwest Kansas/Northwest and North-central
   Oklahoma...
   High-resolution guidance continues to develop storms near the cold
   front and strengthening surface low over northwest OK/south-central
   KS this afternoon/evening in an environment supportive of very large
   hail and damaging winds given ample deep shear and moderate
   surface-based instability. Tornado potential will depend on impacts
   of ongoing storms over central/southern OK, and this will be
   re-evaluated in subsequent outlooks.

   ...Lower to Mid Missouri Valley/Mid to Upper Mississippi Valley...
   The air mass is expected to recover in the wake of overnight
   convection sufficiently to support destabilization during the day. 
   As the cold front advances eastward thunderstorms are expected to
   increase in coverage as height falls/large-scale forcing overspreads
   the area. Pockets of moderate instability and southwesterly shear of
   45-55 kts will support a risk of large hail and damaging gusts with
   the strongest storms.

   ..Bunting/Jewell/Dean.. 05/18/2019

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