SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1252 AM CST Wed Dec 23 2020

Valid 241200Z - 251200Z


Severe thunderstorms are expected across the Mid-Atlantic States
Thursday afternoon and evening. Isolated severe thunderstorms are
also possible across portions of southeast Alabama, southwest
Georgia, and Florida Thursday.

A deep upper trough will extend from western Ontario southwestward
through TX early Thursday morning. A shortwave trough embedded
within the larger upper trough is expected to eject eastward across
the Lower MS Valley before arcing more northeastward into the TN
Valley. Evolution of the embedded shortwave will help induce a
neutral tilt to the upper trough by Thursday afternoon, and a
slightly negative tilt and closed upper circulation over the OH
Valley by late Thursday night/early Friday morning.

The maturing process of the upper trough will also result in further
strengthening of the winds throughout its periphery. By early Friday
morning, 100+ kt 500-mb winds will likely extend from the mid MS
Valley southeastward/eastward through the base of the trough over
the Southeast and then back northeastward into the Northeast. Very
intense low-level flow is also expected, with 60+ kt at 850-mb
extending from the Carolinas through the Mid-Atlantic into Quebec. 

Surface low associated with the embedded shortwave trough is
forecast to begin the period over central AL before racing
northeastward throughout the day. By early Friday morning, this low
will likely be over western NY. This low is also expected to deepen
during the period, helping to induce moisture return across the

...Mid-Atlantic States...
Moisture return ahead of surface low and its attendant cold front is
expected to net low 60s dewpoints across the Carolinas and southeast
VA by the late afternoon/evening. Heating will be tempered by
widespread cloud cover and lapse rates will remain modest. However,
the anticipated moisture return should still be sufficient for
modest instability by the afternoon. At the same time, very
impressive kinematic profiles will be in place over the warm sector,
with 50-70 kt 850+ mb flow contributing to large, looping low-level
hodographs. 0-1 km storm-relative helicity will likely exceed 250
m2/s2 over the warm sector. Any discrete/semi-discrete storms that
develop within this environment should become supercellular and pose
a threat for tornadoes. However, several factors are difficult to
ascertain at this forecast range, including the speed of the cold
front, quality of the moisture return, and coverage of
surface-based, warm-sector storms. These factors preclude
introducing higher tornado probabilities with this outlook, but
upgrades may be needed in subsequent outlooks.  

Additional severe potential will exist along the front as it moves
through the region. Both damaging wind gusts and QLCS tornadoes are
possible along the front as it moves through the region. Higher wind
probabilities may also be needed in later outlooks once the amount
of buoyancy ahead of the front become more certain.

...Portions of GA and FL... 
Modest severe potential is anticipated early Thursday along and
ahead of the front as it moves across the FL Panhandle and southeast
AL/southwest GA. In this region, modest instability and strong flow
will likely support a few strong/severe storms. Similar
environmental conditions, but with less low-level shear, could also
contribute to a few strong/severe storms across the FL Peninsula as
the front moves through.

..Mosier.. 12/23/2020

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