SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0134 PM CST Fri Dec 31 2021
Valid 312000Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MAINLY AFTER
MIDNIGHT FROM SOUTHEAST OK/NORTHEAST TX TO MIDDLE TN/SOUTHERN KY....
...SUMMARY...
Scattered severe thunderstorms remain possible, mainly from late
evening into the overnight across parts of the South-Central States
towards the Tennessee Valley.
...Northern AL/Northwest GA...
There will be a window of opportunity this afternoon for a period of
isolated strong/severe storms to affect northern AL and northwest
GA, within a weakly forced but favorably sheared environment. Refer
to MCD #2089 for further details on this scenario.
...Northeast TX/southeast OK to TN/KY...
The ongoing forecast remains on-track, with no changes made.
Thunderstorms will begin to develop after 10pm across the SLGT risk
area, with the primary severe threat mainly after midnight.
Sporadic hail and wind events may occur overnight in this corridor,
with the potential for a tornado or two if supercell structures can
develop.
..Hart.. 12/31/2021
.PREV DISCUSSION... /ISSUED 1020 AM CST Fri Dec 31 2021/
...Synopsis...
Within a large-scale trough over the western CONUS, one shortwave
trough just off the Baja CA coast will eject east-northeast to the
southern High Plains tonight, in advance of another shortwave trough
digging south-southeastward from the Pacific Northwest to the Desert
Southwest. In response to the ejecting Baja trough, lee cyclogenesis
is expected across southeast CO and northeast NM. This cyclone will
begin to develop eastward along a sharp baroclinic zone late in the
period, as cold air damming occurs across the High Plains.
...Northeast TX/southeast OK to TN/KY and the Deep South...
A broad warm sector has been established for many days from TX into
the Southeast with mid 60s to low 70s surface dew points, and
northward spread of this warm sector is expected through tonight
into southeast OK/AR/TN/southern KY. There is uncertainty regarding
the potential for open warm sector thunderstorm development with
minimal forcing for ascent and some lingering convective inhibition.
However, if a storm or two manage to become sustained later this
afternoon from central MS to northwest GA, the environment will
conditionally favor a supercell severe threat.
Otherwise, increasing low-level moisture along the consolidating
baroclinic zone and strengthening forcing for ascent primarily
through low-level warm theta-e advection will lead to increasing
storm coverage overnight from north TX/southeast OK east-northeast
across AR/TN/KY. Given deep-layer wind fields largely paralleling
the baroclinic zone, elevated convection on the cool side of the
boundary may pose a threat for sporadic severe hail and wind. Any
surface-based storms along or just south of the front will have the
potential to develop supercell structures and to produce a few
damaging gusts, isolated severe hail, and a couple tornadoes from
about 06-12Z.
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