SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CST Wed Dec 30 2020

Valid 311200Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
SOUTHEASTERN TEXAS ACROSS CENTRAL AND SOUTHERN LOUISIANA AND INTO
SOUTHWESTERN MISSISSIPPI...

...SUMMARY...
Severe thunderstorms -- including potential for tornadoes -- are
expected Thursday and Thursday night from southeast Texas into the
lower Mississippi Valley and central Gulf Coast States.

...Synopsis...
An upper pattern featuring split flow will persist across the U.S.
Thursday.  In the southern stream, a low over northern Mexico at the
start of the period is forecast to rotate northeastward and then
northward across central and eastern Texas and into Oklahoma late. 
Meanwhile, a short-wave trough emanating from the northern stream is
forecast to dig rapidly southward across Nevada and California,
eventually evolving into a second low over the southern
Arizona/northwestern Mexico vicinity through latter stages of the
period.

At the surface, the primary feature will be a low initially near the
southern Texas coast.  This low is forecast to deepen gradually
through the day, as it shifts north-northeastward into southeastern
Texas.  Overnight, the northward drift will continue, with the low
reaching eastern Oklahoma/Arkansas and occluding through the end of
the period.  

As the low shifts northward, low-level theta-e advection off the
Gulf of Mexico will occur across the lower Mississippi Valley/Gulf
Coast states, ahead of a cold front which will sweep eastward across
Louisiana and Mississippi through the second half of the period.

...Southeast Texas to Alabama and western parts of Florida
Panhandle...
Showers and scattered thunderstorms will be ongoing at the start of
the period across portions of central and eastern Texas, including a
few stronger/possibly severe storms in the vicinity of the middle
Texas Coastal Plain.  With time, as the surface low deepens and
shifts northward into southeastern Texas, continued influx of higher
theta-e air and very limited heating will permit some
intensification of convection to occur, as storms spread across
southeastern Texas and into Louisiana.  Aiding the convective
intensification/organization will be an increase in both low-level
veering, and deep-layer shear, to the east and northeast of the low
as it begins to occlude.  Along with potential for locally damaging
winds and possibly hail, risk for tornadoes will increase, as shear
becomes increasingly favorable for low-level storm rotation.

With time, threat will diminish from west to east as a cold front
trailing from the northward-moving low advances across east Texas,
and into Louisiana during the evening.  Greatest tornado risk
appears likely to evolve from late afternoon through mid evening,
both ahead of the cold front across southeastern Texas and western
Louisiana, and near a northward-moving Gulf warm front from central
Louisiana into southwestern Mississippi.  

Overnight, some risk will spread into Alabama, and eventually
western portions of the Florida Panhandle, where potential for
locally gusty winds and a tornado or two may linger through the end
of the period.

..Goss.. 12/30/2020

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