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.
Nashville, TN...Birmingham, AL...Little Rock, AR...Chattanooga, TN...Clarksville, TN...
New Orleans, LA...Louisville, KY...Lexington-Fayette, KY...Baton Rouge, LA...Montgomery, AL...
SPC AC 250559
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Thu Mar 25 2021
Valid 251200Z - 261200Z
...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL...EASTERN AND NORTHERN MISSISSIPPI INTO NORTHWESTERN ALABAMA
AND SOUTHERN TENNESSEE...
A tornado outbreak is expected today into early this evening across
parts of the Southeast northward into the Tennessee Valley. Several
long-track strong tornadoes, destructive winds and very large hail
are forecast from the Lower Mississippi Valley, eastward across
parts of the Southeast and northward into the Tennessee and Ohio
...Tornado Outbreak Expected Across Parts of the Southeast and
Tennessee Valley Today into Early This Evening...
...Southeast/Tennessee and Ohio Valleys...
A potent shortwave trough and an associated 75 to 90 kt mid-level
jet will eject quickly northeastward across the southern Plains
today. At the surface, a low will move northeastward and deepen
across the Arklatex and mid Mississippi Valley today. Strong
moisture advection will take place in the lower Mississippi Valley
as a 50 to 65 kt low-level jet strengthens. Surface dewpoints will
increase into the 65 to 70 F degree range by late morning throughout
much of eastern Louisiana, Mississippi and western Alabama. The
low-level moisture combined with surface heating will result in a
moderately unstable and volatile airmass by late morning. A band of
strong large-scale ascent, in advance of the shortwave trough, will
move quickly northeastward across the Arklatex this morning.
Convection appears likely to initiate around midday ahead of this
band of ascent from southeast Arkansas southward into northeast
Louisiana and eastward into southwest Mississippi. This cluster of
thunderstorms is expected to organize and rapidly intensify, moving
northeastward across central and northern Mississippi into
northwestern Alabama during the afternoon. Moderate instability,
strong deep-layer shear and impressive amount of lift on a large
scale will be favorable for widespread severe thunderstorm
development, and a tornado outbreak is expected.
RAP and NAM Forecast soundings this afternoon across the warm sector
from central Mississippi northeastward into northwest Alabama show
an impressive environment for severe storms. MLCAPE is forecast to
increase into the 2000 to 3000 J/kg range across much of central and
northern Mississippi by midday. Surface winds are forecast to become
backed to the south-southeast across the eastern half of
Mississippi. This combined with 60 kt of flow near 850 mb will
result in 0-3 km storm relative helicities in the 400 to 500 m2/s2
range. In addition, the progressive nature of the mid-level jet will
be optimal for the development of tornadic storms. Supercells are
forecast to develop rapidly after initiation across central
Mississippi early this afternoon and move quickly
north-northeastward into northeast Mississippi. Significant tornado
parameter is forecast to increase to near ten across northeast
Mississippi and northwest Alabama by 21Z, making conditions very
favorable for long-track strong tornadoes. As the low-level jet
consolidates and couples with the progressive mid-level jet, a
violent long-track tornado will be possible.
The cluster of severe thunderstorms is expected to move from parts
of northern Mississippi and northern Alabama into the Tennessee
Valley late this afternoon and early this evening. Supercells and
bowing line segments will likely be severe, producing wind damage,
tornadoes and large hail. Hailstones greater than 2 inches in
diameter may occur with the stronger updraft cores. The wind damage
threat is forecast to become more widespread as a squall line
organizes along a cold front in the Mississippi Valley. This line of
severe storms is forecast to move quickly eastward across the Ohio
and Tennessee Valleys this evening, producing widespread wind
damage. Wind gusts of greater than 65 knots will be possible.
Further north in areas near the Ohio River, instability is forecast
to be considerably weaker than in areas to the south. In spite of
the weaker instability, enhanced lift and strong deep-layer shear
will make severe storms possible. As storms move north-northeastward
across the Ohio Valley this evening, isolated large hail and wind
damage will accompany supercells and bow echoes. An isolated tornado
threat will also exist.
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