LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1109 PM CST Mon Nov 28 2022
Valid 291200Z - 301200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS FAR
EAST-CENTRAL LOUISIANA INTO CENTRAL MISSISSIPPI...
...SUMMARY...
Severe thunderstorms capable of producing tornadoes, very large
hail, and a few severe wind gusts are expected this afternoon into
the overnight period across parts of the lower to mid Mississippi
Valley and parts of the Southeast. A few strong tornadoes will be
possible.
...Synopsis...
A surface low will deepen while tracking from Kansas to the Great
Lakes today, accompanied by an eastward advancing upper trough. A
strong mid-level jet stream will overspread an intense low-level jet
across the OH/TN Valleys into the Southeast. As such, strong
deep-layer flow and shear will overlap with a moistening,
destabilizing airmass from late morning to early evening from the
lower MS Valley east-northeastward. Several strong to intense
thunderstorms are expected to organize and promote a relatively
robust severe threat, particularly across the Southeast, where
regionally higher instability should reside.
...Portions of the Lower MS Valley today into early tonight...
Strong warm-air advection should be underway across the Lower MS
Valley at the start of the period (12Z), with rich boundary-layer
moisture being transported northward by a 40-50 kt southwesterly
low-level jet. Through the day, at least modest surface heating
should support surface temperatures rising into the lower 70s F amid
upper 60s F dewpoints within the warm-air advection regime, where an
increase in thunderstorms is also expected. 50-70 kts of
west-southwesterly 500 mb flow and 6.5+ C/km lapse rates will
overspread the lower MS Valley and the warm-air advection regime by
early afternoon, contributing up to 1500 J/kg MLCAPE, which is
adequate in supporting a severe threat.
Storms should eventually root into a gradually deepening boundary
layer during the afternoon, taking advantage of the strong
deep-layer and low-level speed/directional shear provided by the
overlapping southwesterly low-level and westerly mid-level jets.
Large, curved low-level hodographs with mid/upper-level elongation
will support well over 50 kts of effective bulk shear, and 300-400
m2/s2 effective SRH. Supercell structures are expected initially,
with large hail, tornadoes, and a few severe gusts all likely. A few
instances of 2+ inch diameter hail and/or strong tornadoes are
possible with the more robust supercells. Should a more dominant
supercell develop, remain discrete, and traverse an axis of locally
stronger surface heating/buoyancy, a long-tracked and intense
tornado may occur. The latest high-resolution guidance consensus
suggests this scenario would be most likely across central MS, where
a Category 4/Moderate risk is in place. Later at night, storms
should grow upscale into more linear segments as the surface cold
front and greater low-level convergence approaches. Damaging gusts
should then become the main threat, though a few tornadoes remain
possible.
...Parts of the OH/TN Valley into early evening...
A strong surface cold front should sweep across the OH/TN Valleys
through the late afternoon and evening hours as the deepening
surface low tracks across the Great Lakes. Strong convergence along
the cold front should force a low-topped band of convection. Ambient
tropospheric wind fields will be strong, with 55+ kts of flow likely
just 1 km AGL. Downward momentum transport within this line may
foster strong, occasionally damaging gusts, with a couple of severe
gusts also possible, warranting the introduction of Category
1/Marginal probabilities this outlook.
..Squitieri/Darrow.. 11/29/2022
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