SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1157 PM CST Fri Dec 08 2023
Valid 091200Z - 101200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER TO MID MISSISSIPPI VALLEY NORTHEASTWARD INTO THE TENNESSEE
VALLEY...
...SUMMARY...
Severe thunderstorms, capable of producing a few tornadoes,
scattered damaging winds, and large hail, will be possible from the
lower Mississippi Valley northeastward into the Tennessee Valley
this afternoon and evening. Marginally severe storms could also
develop in parts of the Ohio Valley and in the central Gulf Coast
region.
...Lower Mississippi Valley/Tennessee Valley/Ohio Valley...
A positively-tilted mid-level trough and an associated belt of
strong flow will move eastward into the mid Mississippi Valley
today. At the surface, a cold front will advance southeastward into
the mid Mississippi Valley as a moist air mass advects northward
across the central Gulf Coast states and Tennessee Valley. Surface
dewpoints are forecast to increase into the 60s F across northern
Mississippi, northern Alabama and in the western half of Tennessee.
During the day, elevated thunderstorms appear likely to develop on
the northern edge of the moist air mass, with a cluster of storms
moving east-northeastward across northern Arkansas and western
Tennessee. This cluster may be associated with a marginal threat for
hail and wind damage. To the south of this cluster, the airmass
should become moderately unstable by early afternoon, with MLCAPE
peaking in the 1500 to 1800 J/kg range, according to RAP forecast
soundings. During the mid to late afternoon, thunderstorms are
expected to initiate along and ahead of the front, with a gradual
increase in storm coverage taking place across the region.
The eastern edge of the mid-level jet will overspread the warm
sector this afternoon, creating strong deep-layer shear favorable
for severe storms. 0-6 km shear values are forecast to increase into
the 50 to 60 knot range, suggesting supercells will be possible.
Storm-relative helicity in the 200 to 300 m2/s2 range will support a
tornado threat, especially with cells that remain discrete. Although
a tornado threat is expected to develop over a broad area from far
eastern Arkansas northeastward into middle Tennessee, the most
focused tornado potential may be from northwest Alabama into
southern Tennessee. In this area, the combination of low-level shear
and instability is expected to become maximized during the late
afternoon and early evening. In addition to supercells, multicell
clusters and line segments will be likely. The stronger rotating
storms and multicell line segments may be capable of damaging wind
gusts. The large hail threat will likely be associated with the more
widely scattered supercells that develop further west into parts of
the lower Mississippi Valley, where mid-level lapse rates are
forecast to be steeper. The severe threat over the Tennessee Valley
should persist into the mid to late evening as a line segment
gradually develops ahead of the cold front.
Further north into the Ohio Valley, instability is forecast remain
weak in the afternoon and evening with RAP forecast soundings having
MLCAPE peak in the 500 to 800 J/kg range. In spite of this, 0-6 km
shear from 60 to 70 knots will support an isolated severe threat.
Any potential for tornadoes, wind damage and hail is expected to
remain isolated and marginal.
..Broyles/Wendt.. 12/09/2023
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