SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1157 PM CST Fri Dec 31 2021
Valid 011200Z - 021200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF THE LOWER MISSISSIPPI VALLEY TO THE TENNESSEE VALLEY...
...SUMMARY...
Widespread thunderstorms are expected from the ArkLaTex to the
Western Appalachians today. All severe-weather hazards are possible
in parts of these areas, including large hail, damaging winds, and
tornadoes. Strong tornadoes are possible.
...Northeast TX to Western Appalachians...
Late-evening water-vapor imagery depicts a well-defined upper
vort/short-wave trough along the southeast AZ/NM border, shifting
northeast in line with latest model guidance. Dominant upper ridging
over the southeastern US will move little during the day1 period
which will force this short wave across MO into the OH Valley where
it will deamplify within the broader, strong southwesterly flow
regime. Resultant mid-level height falls are not forecast to be that
strong across the warm sector which will encourage the most
concentrated convection to congregate along/near the frontal zone.
Additionally, weak surface low is forecast to track northeast along
the wind shift in response to the ejecting short wave from AR at
daybreak to WV by 02/00z.
Low-level warm advection is currently (0530z) aiding a corridor of
maturing thunderstorms from north-central TX-southeast OK-northern
AR. This activity will likely prove to be the western-northern edge
of strong/severe convection at the start of the period. 00z
soundings across the warm sector were considerably capped this
evening and forecast soundings across portions of the warm sector
later today continue to suggest a relative warm layer near 700mb
which is expected to limit lapse rates through this layer. It's not
entirely clear how much discrete warm sector development will occur
at lower latitudes but wind profiles/low-level shear certainly favor
supercells and tornadoes, and potentially a strong tornado or two.
Higher confidence in thunderstorm coverage exists with frontal
convection. Storm mode will be considerably messy with line segments
and clusters along/near the wind shift. Even a few embedded
supercells can be expected given the observed strong wind fields.
01/00z NAM suggests 65kt LLJ will translate ahead of the short wave
from northern MS/southern AR early, across MS/western TN by 18z,
then into eastern KY by early evening. This reflects the stronger
forcing and likely the primary corridor for more concentrated
strong/severe thunderstorms. Damaging winds and tornadoes are the
primary risks, though some hail may be noted across western/central
portions of the outlook.
..Darrow/Lyons.. 01/01/2022
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