SPC 0700Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1238 AM CST Wed Dec 30 2020

Valid 311200Z - 011200Z


Severe thunderstorms associated with a tornado threat and wind
damage will be possible Thursday into Thursday night from far
southeast Texas into the lower Mississippi Valley and across the
central Gulf Coast States.

...Far Southeast Texas/Lower Mississippi Valley/Central Gulf Coast
An upper-level low will move from northern Mexico into central Texas
on Thursday. The associated upper-level trough will become
negatively-tilted as a 70 to 90 kt mid-level jet rounds the base of
the system. During the day, the moist sector will extend from the
far southeast Texas eastward across Louisiana, southern Mississippi
and southern Alabama. A surface low will move north-northeastward
across the far western edge of the moist sector. Near the surface
low, a large cluster of thunderstorms will be ongoing in the Texas
Coastal Plain at the start of the period. This convection will be
supported by large-scale ascent associated with the nose of the
mid-level jet. The cluster of storms will move east-northeastward to
the upper Texas Coast by afternoon and into the lower Mississippi
Valley by early evening.

Ahead of the cluster of storms, model forecasts increase MLCAPE into
the 500 to 1000 J/kg range over much of the moist sector. In spite
of the weak instability, the mid-level jet will create strong
deep-layer shear profiles, which will be favorable for severe
storms. A severe threat is forecast to first develop in far
southeast Texas early Thursday afternoon as a 50 to 60 kt low-level
jet moves inland across southwestern Louisiana. The severe threat
should be the greatest along and ahead of a pre-frontal trough,
which will progress eastward across southern Louisiana during the
late afternoon and early evening. At that time, low-level shear is
forecast to become maximized due to the presence of the 850 mb jet. 
The jet will create 0-3 km storm relative helicities of 300 to 400
m2/s2, which will support a tornado threat with the more dominant
rotating storms. The tornado threat may become maximized in
southeastern Louisiana during the late afternoon and early evening,
near a pocket of moderate instability. Wind damage will also be
possible with the stronger thunderstorms embedded in the cluster.
The severe threat is expected to continue across southern
Mississippi and southern Alabama during the mid to late evening. The
threat may persist into the early overnight period, especially if a
line of strong thunderstorms can persist.

..Broyles.. 12/30/2020

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