Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 281247
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0647 AM CST Tue Dec 28 2021
Valid 281300Z - 291200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE LOWER MISSISSIPPI DELTA REGION...
...SUMMARY...
Marginally severe thunderstorms are possible this afternoon and
evening over parts of the lower Mississippi Delta region.
...Synopsis...
In mid/upper levels, large-scale troughing will persist over western
North America, as numerous shortwaves pivot through various sectors
of the associated, large cyclonic-flow field. Among those is a
perturbation evident in moisture-channel imagery from western KS
across the TX Panhandle to southeastern NM. This feature should
deamplify and accelerate/eject northeastward today, reaching lake
Michigan by 00Z. Meanwhile, another shortwave trough -- initially
over northern CA and adjacent Pacific waters -- will move
southeastward to southern CA by 00Z, then pivot eastward across the
lower CO River Valley and AZ, reaching NM by 12Z tomorrow.
At the surface, 11Z analysis showed a cold front over south-central
VA, becoming quasistationary across the Appalachians to middle TN,
then a warm front west-southwestward across southeastern OK and
northwest TX. A separate low was drawn over north-central KS, along
a front extending over eastern CO and southeastern NE. The low will
move eastward, while the warm front moves north and merges with the
northern frontal zone. The combined boundary should move southward
as a cold front over the south-central Plains and MO tonight,
reaching the lower Ohio Valley, Ozarks, central/western OK and
southeastern CO by 12Z. The western segment of this boundary should
move northward again as a warm front late in the period over eastern
CO, as the aforementioned shortwave trough approaches.
...Lower Mississippi Delta region and vicinity...
Widely scattered thunderstorms are possible mainly this afternoon
into early tonight, in a plume of low-level convergence and moisture
transport. Damaging gusts and hail near severe limits are possible,
and a marginal tornado threat is apparent as well.
Moisture-channel imagery also indicates a low-latitude perturbation
and associated midlevel UVV field moving north-northwestward from
the Yucatan Peninsula to the south-central Gulf. This feature --
which is expected to approach the mouth of the Mississippi River
around 00Z - will contribute subtle but still supportive DCVA/ascent
to the environment. This, along with rich low-level moisture/
theta-e and diurnal boundary-layer destabilization inland, will
yield MLCAPE around 1000 J/kg potentially as far north as around
I-20, amidst 35-45-kt effective-shear magnitudes. This will support
organized multicells and at least transient supercell potential,
given effective SRH around 100-200 J/kg. The outlook line was
extended inland somewhat in deference to the presence of SBCAPE
farther north, and some erosion of the EML-base stable layer in time
series of forecast soundings. However, the northward extent of
severe potential still will be limited by the associated capping and
weak midlevel lapse rates.
...North TX/southern OK, around 12Z tomorrow...
Isolated to scattered thunderstorms should develop within a couple
hours either side of 12Z tomorrow -- the end of the day-1 forecast
period. Activity will be related to low-level moistening within a
zone of elevated warm advection, beneath suitably steep midlevel
lapse rates to support MUCAPE of 500-1500 J/kg. Forecast soundings
show that, for the more-aggressive destabilization scenarios with
thickest CAPE layers, 45-50-kt effective-shear magnitudes are
possible within the first couple hours after initiation. This
indicates some hail potential may accompany the most-intense cells,
especially around the southern and eastern rim of the convective
plume, where activity will have access to greatest low-level theta-e
and deepest buoyancy. A hail area may need to be added in a future
outlook if confidence increases in activity initiating early enough
to mature to marginally severe levels prior to 12Z.
..Edwards/Gleason.. 12/28/2021
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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