ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 200930
   SPC AC 200930

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0330 AM CST Wed Jan 20 2021

   Valid 231200Z - 281200Z

   ...DISCUSSION...
   Medium-range models are in reasonably good agreement with respect to
   the synoptic-scale features across the U.S. through roughly Day 5
   (Sunday).  Beyond that, increasing divergence in solutions suggests
   insufficient predictability to make any meaningful assessment of
   convective potential.

   Within the Day 4-5 time frame, the primary feature of interest will
   be the large trough situated over the West at the start of the
   period.  More specifically, a short-wave feature moving through the
   broader-scale cyclonic flow -- which is progged to lie near the
   central California coast at the start of Day 4 -- will substantially
   influence convective potential in the medium range.

   Day 4 (Saturday), this short-wave feature is forecast to shift
   southeastward, moving into the southwestern U.S./northern Baja
   during the overnight hours.  As this occurs, an increase in
   southerly low-level flow is progged over the southern Plains.  This
   trend will continue into Day 5, as the upper system shifts eastward
   and crosses northern Mexico/Arizona/New Mexico -- but while
   weakening steadily as it progresses eastward.  In response, rather
   ill-defined cyclogenesis is expected to occur over the Texas
   vicinity.  As ascent increases and low-level moisture advection
   continues, an increase in convective potential will occur across the
   southern Plains and into the lower Mississippi Valley.  However,
   despite favorable shear that would otherwise support severe
   potential, some likelihood for persistent/weak boundary layer
   stability beneath low-level capping is a concern.  Still, some
   severe potential could evolve, possibly focused along a weak
   east-to-west warm frontal zone across east Texas and the Arklatex
   region later Sunday and into Monday.  However, degree of risk
   remains questionable at this time, such that an outlook area will
   not be introduced at this time.  

   By Day 6 (Monday), the weakening upper system is progged by the GFS
   to essentially dampen out with time, as it crosses Oklahoma and
   Kansas, and shifts into Missouri.  Meanwhile, the ECMWF maintains a
   much more well-defined feature, that moves quickly across the Ozarks
   and Mid Mississippi Valley by evening, and then into/across the
   Carolinas and Virginia by the end of the period.  Along with this
   more pronounced upper feature, a corresponding/well-developed
   surface cyclone is also progged to cross the southeastern quarter of
   the country Monday, suggestive of at least some severe potential
   spreading eastward across this region should the pattern evolve more
   similar to the ECMWF solution.  

   At this time however, given the increasing model differences beyond
   Day 5/Sunday, no severe-weather assessment will be attempted through
   the remainder of the medium-range period.

   ..Goss.. 01/20/2021

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