SPC AC 201225
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0625 AM CST Thu Jan 20 2022
Valid 201300Z - 211200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Severe thunderstorms are not forecast across the contiguous United
States today.
...Synopsis/Discussion...
In mid/upper levels, a series of nearly phased shortwaves will
result in positively tilted troughing shifting eastward across
eastern Canada, the Great Lakes region, the central/southern Plains,
and northwestern/north-central MX through this period. Substantial
associated mid/upper-level forcing for ascent is expected to remain
well behind an associated surface cold front -- analyzed at 11Z from
southern New England across central VA, northern GA, to a weak low
over coastal MS, then southwestward across the northwestern Gulf to
near BRO. By 00Z, the front should extend from just off the NC
Outer Banks southwestward across southern GA, the central/eastern FL
Panhandle, and the central/southwestern Gulf. By 12Z tomorrow, the
front should reach northern FL and the south-central Gulf, while
decelerating.
As this front progresses along the central/eastern Gulf Coast today,
it will encounter an immaturely modified boundary layer still
retaining a good deal of continental/polar characteristics from
behind prior frontal near the front, supported by low-level moisture
manifest as warm-sector dew points in the 60s along the coast. Weak
mid/upper-level lapse rates will limit buoyant depth, which (along
with weak surface winds veering with time) will limit effective-
shear magnitudes, keeping them at around 20-35 kt -- considerably
less than fixed-layer (0-6-km) shear. Between that factor,
potentially messy storm modes under strongly front-parallel flow
aloft, and weak buoyancy (MLCAPE generally under 500 J/kg), severe
potential appears too low and conditional for any categorical areas.
Isolated thunderstorms also will be possible over parts of south FL
and the Keys, mainly late this afternoon into early evening. Richer
low-level moisture -- now prevalent across the Keys and southern
Straits -- should spread somewhat northward. Forecast soundings
suggest enough boundary-layer moisture to support MLCAPE near 500
J/kg, some of which briefly may reach into layers supporting
lightning generation -- albeit with weak lapse rates continuing in
the mid/upper levels. Winds will veer with height, but remain weak
below about 800 mb, limiting low-level shear. Lack of stronger
values of both buoyancy and shear will preclude an organized severe
threat.
..Edwards/Broyles.. 01/20/2022
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