SPC AC 010727

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0227 AM CDT Mon May 01 2017

   Valid 031200Z - 041200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM
   CENTRAL/SOUTHERN TEXAS EASTWARD TO LOUISIANA...

   ...SUMMARY...
   A few severe storms will be possible from central/southern Texas
   eastward to Louisiana on Wednesday.

   ...Synopsis...
   With multiple shortwave impulses progressing east/southeast across
   the central US, a longer-wave trough will gradually amplify across
   the Plains states and Mississippi Valley through Wednesday night.
   Meanwhile, upstream ridging will overspread the Inter-Mountain West.

   ...Central/southern Texas eastward to parts of Louisiana...
   In response to a weak shortwave trough embedded in the southern
   stream, convection will likely be ongoing/expanding across parts of
   southeast Texas and potentially southwest Louisiana on Wednesday
   morning. With a plume of relatively steep mid-level lapse rates over
   much of the region and a veering wind profile with height, stronger
   cores may be capable of a few severe hail reports early in the day.
   Additionally, a tornado may be possible near a warm front close to
   the upper Texas Coast / Sabine Valley, where any surface-based
   updrafts would encounter enhanced storm-relative helicity. Of note,
   most guidance has trended westward and slightly narrower with the
   warm/moist sector supportive of such surface-based development.
   Considering ample subsidence/drying behind the current highly
   amplified central/eastern US system, this trend does not appear
   unreasonable. As such, confidence in anything more than marginal
   severe probabilities remains low for this early convection. 

   Farther north, weak warm advection and/or convergence along a front
   pushing east/southeast will likely encourage convection across parts
   of north Texas eastward to the Ark-La-Tex through the morning and
   afternoon hours. Modest mid-level flow and weak/moderate buoyancy
   will likely yield a threat for a few instances of severe hail and
   perhaps strong wind gusts.

   More substantial buoyancy will likely materialize across portions of
   central/southern Texas during the afternoon hours, as surface dew
   points in the upper 60s/lower 70s combine with diurnal heating to
   yield upwards of 2000-3000 J/kg of MLCAPE. While some guidance
   suggests even greater buoyancy potential, the aforementioned
   early-day convection offers uncertainty regarding this upper-end
   scenario. Furthermore, weakened/veered 850-700mb flow in the wake of
   the initial impulse appears somewhat unfavorable for widespread
   organized updrafts. As such, thunderstorms are forecast to develop
   into clusters/segments along the cold front pushing southeast
   Wednesday afternoon/evening, with the potential for at least a few
   instances of large hail and strong winds. Considering the potential
   for moderate/strong buoyancy, some portions of the region could be
   upgraded to a Slight Risk in later outlooks as mesoscale details
   become clearer.

   ..Picca.. 05/01/2017

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