SPC 0700Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1255 AM CST Tue Dec 22 2020

Valid 231200Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MIDDLE
TX COAST EASTWARD ACROSS MUCH OF LA...MS...AL AND FL PANHANDLE...

...SUMMARY...
Isolated severe thunderstorms are possible from the middle Texas
Coast across much of Louisiana, Mississippi, Alabama, and the
Florida Panhandle.

...Synopsis...
A deep upper trough is expected to extend from the Canadian Prairie
Provinces southwestward into the Four Corners early Wednesday
morning. Several shortwave troughs will rotate through this parent
upper trough, contributing to both eastward progression and
continued deepening. Upper flow around the trough will also
strengthen significantly throughout the period, with a corridor of
100+ kt 500-mb winds expected from the Lower MS Valley into southern
Ontario by early Thursday morning.

At the surface, low associated with the lead shortwave embedded
within the larger upper trough will begin the period centered over
east-central MN/northwest WI. A strong cold front will extend from
this low southwestward through the Mid MO Valley and OK into
southwest TX. Fast eastward/southeastward progression of this front
is expected throughout the day, and the front will likely extend
from eastern Lower MI south-southwestward into the western FL
Panhandle by 12Z Thursday.

Moisture return is anticipated ahead of this front, with low 60s
dewpoints likely in place before frontal passage from the middle TX
Coast eastward along the central Gulf Coast and into the FL
Peninsula. Abundant cloud cover ahead of the front will limit
heating and lapse rates will remain poor, resulting in only modest
buoyancy. In addition, much of the pre-frontal activity will be
induced by warm-air advection and elevated above a shallow stable
layer. That be said, surface-based storms do appear possible along
the coastal areas of the middle and upper TX coast eastward along
the central Gulf Coast and into the FL Peninsula where dewpoints may
reach the mid 60s. 

Low to mid-level wind fields will be strong, supporting stronger
storms with any more persistent and deep updrafts. Any tornado
threat will be confined to areas mentioned above where surface-based
storms are most likely. Uncertainty is too high to introduce 5%
tornado probabilities with this outlook, but two areas may merit an
upgrade in later outlooks. One is along the middle/upper TX coast
where mid 60s dewpoints and modest heating may result in greater
instability. The other is over the FL Panhandle and adjacent
southern AL where strong low-level flow is anticipated early
Thursday morning. 

Additionally, damaging wind gusts are possible along and just ahead
of the front as it moves across the Southeast. Much of this threat
will be north of the warm front, but occasional gusts should be able
to penetrate the shallow stable layer and manifest at the surface.

..Mosier.. 12/22/2020

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