SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1128 AM CST Sat Dec 12 2020

Valid 131200Z - 141200Z


Isolated strong to severe thunderstorms may impact parts of the
Upper Texas Coast and southern/central Louisiana on Sunday. Damaging
wind gusts and perhaps a tornado or two should be the main threats.

...Upper Texas Coast into Southern/Central Louisiana...
A southern-stream shortwave trough is forecast to dig across the
southern Plains on Sunday, eventually reaching the Southeast late
Sunday night. Strong mid-level height falls preceding this shortwave
trough will encourage surface cyclogenesis along/near the Upper TX
Coast through Sunday afternoon, with this weak low gradually
deepening as it moves northeastward across the lower MS Valley and
Southeast through the period. A warm front extending to the
east/northeast of the surface low should make some northward
progress across portions of coastal southeast TX and
southern/central LA by Sunday evening. A small warm sector should
develop through the day across this area, as modest diurnal heating
and surface dewpoints in the low to mid 60s support MLCAPE generally
in the 250-500 J/kg range. This weak instability, which will extent
through the near-surface layer, will probably be sufficient to
support surface-based thunderstorms.

A strong wind profile through the troposphere associated with the
shortwave trough will likely support 40-50+ kt of effective bulk
shear over the warm sector. This will be more than sufficient for
supercell structures, although weak mid-level lapse rates may limit
more vigorous updrafts to some extent. Isolated to scattered
convection should develop by early Sunday afternoon as a low-level
jet strengthens, and this activity will move quickly
east-northeastward into LA by Sunday evening along/ahead of a cold
front. Occasional damaging straight-line winds should be a concern
given the strength of the low/mid-level flow, and with the potential
for storms to grow upscale into a small bowing line segment. A
tornado or two also appears possible, as a veering low-level wind
profile and related shear appear sufficient for rotating updrafts.
Convection should have a tendency to become elevated into MS/AL as
it outpaces the greater low-level moisture in LA, with a lower
severe threat Sunday night across the Southeast. Weak forecast
instability precludes greater severe wind/tornado probabilities at
this time.

...Coastal Alabama into the Western Florida Panhandle...
There may be a narrow corridor of surface-based storm potential
along the immediate coastal portions of AL and the western FL
Panhandle late Sunday night as mid to perhaps upper 60s surface
dewpoints return northward. However, the stronger forcing for ascent
attendant to the shortwave trough will likely remain to the north of
this area. Forecast soundings from various guidance also suggest
that a low-level inversion may inhibit robust thunderstorm
development with southward extent across the Southeast.

..Gleason.. 12/12/2020

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