SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Fri Mar 18 2022
Valid 181200Z - 191200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST MISSISSIPPI...ALABAMA...FAR WESTERN FLORIDA PANHANDLE AND
FAR WESTERN GEORGIA...
...SUMMARY...
Severe thunderstorms are expected today across the central Gulf
Coast states, where tornadoes, wind damage and isolated large hail
will be likely with the strongest of storms. Storms with large hail
and wind damage may also occur further north across the Ohio and
Tennessee Valley, some of which could have very large hail.
...Southeast...
A progressive upper-level trough will move quickly
east-northeastward from the southern Plains into the Arklatex and
Ozarks today, as a 60 to 80 knot mid-level jet translates
northeastward from the lower Mississippi Valley into the Tennessee
Valley. At the surface, a warm front will move northeastward across
the central Gulf Coast States. This warm front will be an important
player for the severe threat. To the southwest of the warm front,
surface dewpoints will be in the 60s F, contributing to a broad warm
sector with moderate instability. Thunderstorms associated with a
substantial severe threat, will be ongoing at the start of the
period from central Mississippi south-southwestward into
southeastern Louisiana. These storms will move northeastward across
the central Gulf coast states during the morning into early
afternoon.
A low-level jet should be positioned over southern Mississippi at
daybreak with the jet moving northeastward into central Alabama by
midday. This feature combined with the mid-level jet will create
strong deep-layer shear favorable for supercells. Forecast soundings
from southeast Mississippi northeastward into south-central Alabama
in the 15Z to 18Z time frame have 0-3 km storm relative helicity in
the 300 to 400 m2/s2 range suggesting conditions will be ideal for
tornadoes. If supercells can track northeastward at nearly the same
speed as the warm front, then a long-track strong tornado will be
possible. Other tornadic storms will be possible with cells that
interact with the warm front. Isolated wind damage and large hail
will also be likely with the more dominant supercells. There is some
concern with the weak storm relative winds at mid-levels evident on
forecast soundings across parts of central Alabama. This would be
prone to have downdrafts raining down into the updrafts. But still
some storms, with access to the strongest of instability on the
southern edge of a large area of rain, should be able to maintain
strong updrafts and maintain a persistent severe threat.
...Ohio and Tennessee Valleys...
An upper-level low will track eastward across the lower Missouri
Valley today as the left exit region of a 60 to 80 knot mid-level
jet moves across the Ohio Valley. At the surface, a 1000 mb low will
track east-northeastward across the mid Mississippi Valley. A narrow
corridor of maximized low-level moisture will be in place from
western Tennessee into southern Missouri, where surface dewpoints
will be in the 50s F by late morning. Scattered thunderstorms are
expected to form from this corridor eastward into the lower Ohio
Valley this afternoon, where 700-500 mb lapse rates will be steep
and large-scale ascent will be strong. This should be favorable for
relatively low-topped supercells with isolated large hail. A few of
the storms could produce hailstones of greater than 2 inches in
diameter. An isolated wind-damage threat could also develop with the
stronger supercells. The area with the greatest threat for very
large hail will be from far southeast Missouri northeastward across
western Kentucky and into far southern Indiana. In this area, lift
associated with the mid-level jet, instability and mid-level lapse
rates will be most favorable.
..Broyles/Squitieri.. 03/18/2022
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