Day 4-8 Outlook

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0357 AM CST Sun Dec 27 2020

Valid 301200Z - 041200Z

...DISCUSSION...
...Wednesday/Day 4 and Thursday/Day 5...
The medium-range models move an upper-level trough across the
southern Rockies and central High Plains on Wednesday. At the
surface, a cold front is forecast to advance southeastward into the
mid Mississippi Valley and Arklatex. Thunderstorms appear likely to
develop along and ahead of the front during the day due to weak
destabilization and strong large-scale ascent. Moisture advection is
forecast to continue during the day across the lower Mississippi
Valley in the presence of a pronounced low-level jet. In spite of
weak instability, very strong wind profiles associated with the low
to mid-level jet structure, could enable thunderstorms that obtain a
severe threat. Cells that initiate well to the east of the front
across the moist sector will have potential to become supercells.
The main threat would be for a few tornadoes and isolated wind
damage. The potential appears great enough to add a 15 percent
contour for parts of the lower Mississippi Valley.

On Thursday, an upper-level low is forecast to develop in the
southern Plains. In response, the low-level jet in the central Gulf
Coast states is forecast to strengthen. Thunderstorms will be
possible in the Tennessee Valley and central Gulf Coast states along
the axis of the low-level jet and further to the west, along the
cold front. Instability is forecast to remain weak from Wednesday
into Thursday. However, strong wind profiles should offset this
limitation, with the possibility of a severe threat continuing into
Thursday. The main severe weather potential would be for an isolated
tornado and wind damage threat with clusters that organize during
the day. The wind damage threat could become more widespread if a
squall-line can develop across the region. A 15 percent contour has
been added to parts of the central Gulf Coast for Thursday to
account for this possibility.

...Friday/Day 6 to Sunday/Day 8...
Southwest mid-level flow is forecast to be maintained from the
Southeast to the Eastern Seaboard on Friday. A cold front is
forecast to move eastward across the eastern Gulf Coast States and
Carolinas. Thunderstorm development will be possible along and ahead
of the front. Surface dewpoints in the 60s F along with weak
instability and strong deep-layer shear could be enough for an
isolated severe threat.

On Saturday and Sunday, the system is forecast to move eastward to
the Eastern Seaboard as surface high pressure dominates across much
of the continental United States. For this reason, thunderstorm
potential is expected to be minimal over the weekend in most areas.

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