ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 110958
   SPC AC 110958

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0358 AM CST Thu Mar 11 2021

   Valid 141200Z - 191200Z

   ...DISCUSSION...
   ...Sunday/Day 4 and Monday/Day 5...
   The medium-range models move an upper-level low across the central
   Plains on Sunday. At the surface, a low is forecast to deepen across
   the southern High Plains as a cold front advances quickly eastward
   into the Ozarks and Arklatex. A squall-line appears likely to
   develop just ahead of the front, moving eastward into the lower to
   mid Mississippi Valley by early evening. Model forecasts continue to
   show weak instability ahead of the squall-line. This should keep any
   severe threat somewhat isolated, except in areas that develop
   locally greater instability. Wind damage and hail will be possible
   along the stronger parts of the squall-line. An isolated tornado
   threat will also be possible.

   On Monday, the models are in much better agreement. The upper-level
   low is forecast to move into the mid Missouri Valley as a cold front
   advances quickly eastward into the Tennessee Valley and central Gulf
   Coast states. A remnant of the squall-line may be ongoing ahead of
   the front in the morning. This line may re-intensify by midday as
   instability increases. The current thinking is that an isolated wind
   damage threat will develop during the afternoon from middle and
   eastern Tennessee southward into Alabama.

   ...Tuesday/Day 6 to Thursday/Day 8...
   Model spread increases on Tuesday as the pattern becomes less
   amplified. An upper-level trough is forecast to move into the
   southern High Plains with some moisture return occurring in the
   southern Plains. The moist air mass is forecast to extend eastward
   from east Texas across much of the Gulf Coast states. Thunderstorms
   will be possible along the northern edge of this moist air mass
   throughout much of the day. The greatest instability is forecast
   across east Texas and Louisiana, where a severe threat could
   develop. However, the models differ on the northward extent of the
   moist air mass. The GFS is more aggressive with moisture return,
   suggesting the severe threat could be as far north as the Red River.
   However, uncertainty is high concerning this scenario.

   On Wednesday, the model solutions sharply diverge. The GEFS also
   shows considerable spread among the members. Among the deterministic
   models, the GFS continues to be an aggressive solution, moving the
   upper-level trough across the Great Plains. An associated cold front
   is forecast to move into the Ohio and Tennessee Valleys. Severe
   thunderstorms would be possible on the southern part of the front
   from Tennessee southward to the Gulf Coast. In contrast, the ECMWF
   confines the moist airmass to the coastal areas of the Southeast,
   which would be less favorable for severe storms. A cool and dry air
   mass is forecast on Thursday across much of the nation. This could
   limit the severe potential.

   ..Broyles.. 03/11/2021

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