SPC
 
...Day5/Saturday - Mid South and the Tennessee Valley to the
   Southern Appalachians...
   Severe weather will likely be ongoing at the beginning of the period
   from the early morning thunderstorms across Arkansas and vicinity.
   There may be a slight lull in storm coverage/intensity during the
   diurnal minimum Saturday morning, as the lead wave continues
   northeastward and the primary trough approaches from the west.
   However, by midday, significant height falls will start to
   overspread the warm sector and widespread storm development is
   anticipated. The location of overnight convection will have a
   significant impact on the zones within the broader risk area where a
   higher severe weather threat will exist. However, all guidance shows
   a broad warm sector with a broad 50 knot low-level jet, which would
   foster an environment favorable for all severe weather types. The
   greatest uncertainties are related to the northward extent of the
   risk and the surface low track. Given the widespread convection
   expected north of the warm front, a convectively reinforced warm
   front could set up farther south than the surface low track may
   suggest. Also, global guidance still varies with the intensity and
   location of the surface-low as it tracks northeast. The track and
   intensity of this surface-low will have some impact on the storm
   evolution and intensity within the warm sector, especially as it
   relates to storm mode and the tornado threat. Maintained 15 percent
   probabilities from the previous Day 6 forecast with an expansion on
   the southern and eastern extent to account for the threat continuing
   late Saturday night. 
   ...Day6/Sunday - Portions of the Southeast into the Carolinas...
   A severe-weather threat will likely persist into the Southeast and
   Carolinas after 12Z on Sunday, but the magnitude of the threat
   varies greatly. Most guidance shows a remnant squall line moving
   through the region. With extensive cloud cover, slightly lower
   moisture quality, and decreasing ascent, a significant severe threat
   would not necessarily be most likely. However, there is still
   considerable uncertainty during the Day 6 timeframe, and several of
   the GEFS members, including the operational GFS, have a deepening
   surface cyclone somewhere east of the Appalachians on Sunday. This
   would lead to a more significant severe-weather threat than ECMWF
   guidance would suggest and will need to be monitored as a
   possibility.
   ..Bentley.. 12/28/2021