SPC AC 121729

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CST Fri Mar 12 2021

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
   EASTERN TX PANHANDLE INTO WESTERN OK/NORTHWEST TX...

   ...SUMMARY...
   Scattered severe thunderstorms are expected across the Oklahoma and
   Texas Panhandles, northwest Texas, and western Oklahoma on Saturday,
   with the greatest threat expected from mid afternoon into the early
   evening. A few tornadoes, including the possibility of a strong
   tornado, and very large hail will be the primary hazards, with
   damaging wind gusts possible as well.

   ...Synopsis...
   A large mid/upper-level low approaching the Four Corners region at
   the start of the period Saturday morning is expected to move
   east-northeastward and gradually deepen through the day, before
   reaching a position centered near eastern CO by early Sunday
   morning. In conjunction with the upper low, a surface cyclone is
   expected to gradually deepen during the day as it moves from
   southeast NM into the central High Plains. A surface boundary
   initially draped from the TX South Plains into central OK is
   expected to move northward as a warm front in conjunction with the
   surface cyclone.

   ...Portions of the Central/Southern High Plains...
   Elevated convection will likely be ongoing Saturday morning
   somewhere north of the surface boundary, from far eastern NM into
   the TX/OK Panhandles and southwest KS. Instability and shear will be
   sufficient to support some threat of hail and perhaps locally
   strong/severe wind gusts with the strongest storms during the early
   morning hours. 

   The primary severe threat is expected to develop later in the day,
   near and south of the northward-moving warm front and east of a
   dryline that is expected to develop and begin moving eastward across
   the OK/TX Panhandles into the TX South Plains by early afternoon.
   Dewpoints in the upper 50s/low 60s F beneath steep midlevel lapse
   rates will support MLCAPE of 750-1500 J/kg by mid afternoon, with
   somewhat higher values possible depending on the extent of heating
   that can occur across the warm sector. Convergence near the triple
   point and southward along the dryline, and broadly difluent
   mid/upper-level flow, should support surface-based thunderstorm
   development by early afternoon across the TX Panhandle, and perhaps
   across adjacent portions of the OK Panhandle and TX South Plains.

   Effective shear of 50-70 kt across the warm sector will be more than
   sufficient to support organized severe thunderstorms. Initial
   development will likely evolve into discrete or semi-discrete
   supercells, with an initial threat of large hail (potentially
   significant). Substantial veering of the low-level wind profile and
   an increasing southerly low-level jet will support effective SRH of
   200-400 m2/s2, which will support a tornado threat with any
   supercells moving northeastward into the eastern TX Panhandle,
   western OK, and western north TX, where somewhat greater buoyancy is
   expected to reside. 

   The primary uncertainties at this time regarding significant severe
   potential are the northward extent of the warm front, which will
   determine the northern boundary of the greatest threat, and the
   duration of any discrete or semi-discrete supercell threat, with
   somewhat meridional mid/upper flow and increasing large-scale ascent
   ahead of the upper low likely to result in cell mergers and upscale
   growth by early evening. However, given the potential for at least a
   few hours of discrete supercell activity within a very favorable
   kinematic environment, have opted to include an Enhanced Risk
   upgrade driven by the potential for strong tornadoes and very large
   hail. Some adjustment/expansion of the greatest threat area, and
   potentially an additional upgrade, will be possible in subsequent
   outlooks if guidance and observational trends continue to favor the
   potential for a few longer-track supercells in the warm sector.  

   An increasingly linear band of convection will support a threat of
   damaging wind and perhaps a brief tornado or two into south-central
   KS/west-central OK/north-central TX Saturday night, before rapidly
   weakening instability with eastward extent reduces the severe
   threat. Some backbuilding is also possible into portions of
   southwest TX during the evening, with a primary threat of hail and
   damaging wind.

   ..Dean.. 03/12/2021

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