SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0654 AM CST Tue Feb 22 2022
Valid 221300Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
MID-SOUTH...LOWER OHIO VALLEY...TENNESSEE VALLEY...MISSISSIPPI...AND
ALABAMA....
...SUMMARY...
Damaging thunderstorm gusts, a few tornadoes, and isolated severe
hail are possible today from Arkansas to the Mid-South and lower
Ohio Valley, and this evening over parts of Mississippi, Alabama and
Tennessee.
...Synopsis...
In mid/upper levels, mean troughing and extensive cyclonic flow will
be maintained over the West through the period, but with an embedded
pattern shift toward split flow. This will occur as a strong, cold
shortwave trough -- evident in moisture-channel imagery over OR and
northern CA -- pivots southeastward and evolves into a closed
cyclone tonight over NV. In response to these developments, a broad
fetch of southwesterlies aloft will be maintained from the
southern/central Rockies across the southern/central Plains,
Midwest, Great Lakes and Southeast. An embedded shortwave trough --
initially located from southern KS to west TX -- will move
northeastward and weaken. This feature should stretch into a
remnant vorticity banner from the Ozarks to north-central and
southwest TX by 00Z, weakening further while aligning from the Ohio
Valley back to the Red River by 12Z tomorrow.
At the surface, 11Z analysis showed an intense cold front extending
from an elongated area of low pressure over western IL to central
MO, southwestward across eastern OK, the TX South Plains, and
extreme east-central/northeastern NM. By 00Z, the low should
consolidate and reach eastern Lower MI, with cold front over western
OH, western TN, northern LA, south-central/southwest TX, and east-
central/north-central NM. By the end of the period, the front
should reach eastern NY, western VA, northwestern GA, southwestern
MS, deep south to far west TX across some adjoining portions of MX,
and central NM.
...AR to Ohio Valley today...
A belt of strong-severe convection, with a fast-moving, leading
squall line, is ongoing across portions of the Mid-South. This
activity will proceed northeastward to parts of the Ohio Valley,
western/mid TN, and western/central KY this morning, encountering an
environment of weak but adequate low/middle-level instability,
surface dew points in the mid 50s to low 60s F, long hodographs and
low-level shear vectors, and strong deep shear. Damaging gusts, a
few tornadoes, and isolated, marginally severe hail are possible.
Trailing convection in the associated belt of prefrontal/low-level
lift also may pose a severe threat. Refer to SPC tornado watch 25
and related mesoscale discussions for near-term details on the
morning scenario. As the associated hodograph-enhancing LLJ shifts
rapidly northeastward toward the central/northern Appalachians
today, two processes are expected:
1. The initial MCS will outrun a narrowing surface-based warm
sector in its path, encountering progressively weaker inflow-layer
buoyancy, and weaken across northeastern fringes of the outlook
area.
2. Low-level shear will decrease substantially, but remain at least
marginally favorable for any trailing/lingering convection in the
plume, that can access diurnally heated and relatively undisturbed
surface-based effective-inflow parcels. However, in the absence of
substantial large-scale lift/support, and with flow aloft parallel
to a sagging outflow boundary, messy/training convection with a
slightly anafrontal boundary regime will make the severe threat more
conditional and marginal into mid/late afternoon.
...MS/AL/TN this evening...
Some rejuvenation of a LLJ-associated plume of low-level convergence
and convective potential is expected this evening, as the boundary
layer decouples, but before it cools/stabilizes too much to support
surface-based thunderstorms. Despite lack of substantial mid/upper-
level forcing for ascent, warm advection, moisture transport and
related favorable low-level theta-e will support thunderstorm
development, amid weak CINH and lingering favorable deep shear.
Forecast soundings suggest 500-1000 J/kg MLCAPE will be possible in
a triangular swath bounded on the east by more-stable, recycled
continental/polar air, the cold front and EML-related MLCINH on the
northwest/west, and weaker lift/greater CINH to the south. Though
not as large as with the morning regime farther north, well-shaped
hodographs and 45-55-kt effective-shear magnitudes will support
supercell potential, as well as embedded small bow/LEWP formations.
Damaging gusts and a couple tornadoes may occur before lift and
instability weaken overnight, ramping down the severe threat.
..Edwards/Gleason.. 02/22/2022
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