Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1131 AM CST Fri Dec 27 2024
Valid 281200Z - 291200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF EAST TEXAS...THE LOWER MISSISSIPPI RIVER VALLEY INTO THE
TENNESSEE VALLEY...
...SUMMARY...
A regional outbreak of severe storms, with large hail, damaging
winds, and strong tornadoes is possible Saturday into Saturday
night, from East Texas, across the Lower Mississippi Valley, into
parts of the Tennessee Valley.
...Synopsis...
Mid-level flow is expected to rapidly amplify over the southern
CONUS Saturday, as several southern stream perturbations intensify
as they move near the Gulf Coast. A prominent shortwave trough,
initial located across the southern OH Valley, will quickly eject
northward as a second stronger shortwave approaches from the
southern Plains vicinity. A roughly east-west oriented warm front
will quickly move inland overnight Friday and into early Saturday in
response to increased mid-level height falls and a deepening surface
low near the Red River. This will allow for robust moisture return,
with upper 60s to low 70s F dewpoints likely across the lower MS
Valley by daybreak. While clouds and precipitation from inland
moisture advection may complicate destabilization to some degree,
sufficient buoyancy is expected to support numerous strong to severe
storms with all hazards possible from East TX and the lower MS
valley, into the TN valley from Saturday morning into early Sunday.
...East TX, Lower MS Valley...
As the mid-level flow pattern quickly amplifies Saturday, the
prominent shortwave trough and a subtle lead wave over the southern
plains should rapidly strengthen, taking on neutral to slightly
negative tilts by 00z Sunday. As this occurs, increasingly strong
diffluent flow aloft will overspread East Texas toward the ArkLaMiss
vicinity, where middle 60s F surface dewpoints will become more
common. Steepening low/mid-level lapse rates and diurnal heating
should allow for moderate destabilization, despite some lingering
clouds and isolated elevated storms.
Deeper convection is expected to develop early in the period
(11-14z) as ascent from the embedded perturbation and main trough
move over a pre-frontal confluence axis across East TX/Western LA. A
second round of robust convection may also develop across eastern TX
later in the afternoon as a Pacific front associated with the
surface low over North TX impinges on the warm sector from the west.
A mix of semi-discrete supercells and linearly organized bowing
segments are expected with sufficient buoyancy/deep-layer shear
overlap for storm organization. An initial risk for large hail,
especially where low-level flow is somewhat veered, should
transition to a risk for damaging winds and tornadoes as 0-1 km SRH
increases to 150-300 m2/s2 into mid/late Saturday afternoon with a
35+ kt 850 mb low-level jet.
Convection should quickly spread northeast into the lower MS Valley,
peaking in intensity through the afternoon and early evening hours.
Coincident with an increase in the low-level jet to 45-65 kt and
intensifying surface pressure falls, low-level hodographs will
expand with 0-1 km SRH of 300-400 m2/s2 likely. This will support
the potential for strong tornadoes with any established
suppercellular elements.
...Tennessee Valley and Cumberland Plateau...
As the upper trough continues to amplify through the day, the warm
front will gradually lift north into the southern TN valley by early
afternoon. A broad area of cloud cover and perhaps light stratiform
precipitation is expected in the presence of strong isentropic
ascent along the advancing warm front. This remains the primary
uncertainty regarding the northern/eastern extent of the
surface-based severe risk later Saturday afternoon into Saturday
night. While buoyancy/destabilization may be muted, the intensifying
upper trough and surface low will favor very strong low and
mid-level wind fields supportive of storm organization into Saturday
evening and early Sunday. With very large low-level hodographs (0-1
km SRH 300-500 m2/s2) weakly buoyant near-surface based parcels will
still allow for some tornado and or damaging wind risk into the
overnight hours, especially with any established supercell or bowing
structures across parts of AL, TN and western GA.
