SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0155 PM CST Wed Feb 12 2025
Valid 122000Z - 131200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
LOUISIANA MISSISSIPPI AND ALABAMA...
...SUMMARY...
Severe thunderstorms are expected to continue this afternoon through
late tonight from the Lower Mississippi Valley into western GA. The
main potential is for damaging winds and tornadoes, a few of which
could be strong (EF2+).
...20z Update...
The prior forecast remain valid with only minor changes to the
thunder area over parts of east TX and parts of AR. Multiple bands
of convection along the surging cold front over the Sabine Valley
should continue to steadily intensify as broad height falls from the
advancing trough overspread the western edge of the warm sector
characterized by surface dewpoints in the upper 60s to low 70s F.
These storms should eventually coalesce into a broader QLCS as the
front accelerates. 50-60 kt of deep-layer shear will support
organization into bowing segments and embedded supercell structures.
Damaging winds and a couple tornadoes appear likely.
Farther east over southern LA, MS and AL, strong low-level warm
advection is occurring in the vicinity of an east-west oriented warm
front and weak frontal cyclone rapidly lifting north over the
southern Gulf Coast. As ascent intensifies with the approach of the
upper trough, strong observed pressure falls of 2-3 mb per hour will
rapidly advect pristine upper 60s to low 70s F surface dewpoints
(evident on the 18z LIX sounding) northward. Several bands of
convection (including a few supercells) have developed and should
continue to intensify through the afternoon. The rapid air mass
modification/destabilization will overlap with substantial vertical
shear, supporting supercells capable of all hazards, including a
strong tornado.
The severe threat will likely persist through the evening and
overnight hours as the emerging QLCS shifts eastward in the
narrowing warm sector over eastern AL and western GA. Despite waning
buoyancy, continued advection of near 60 F surface dewpoints and
very strong low-level shear (ESRH 300-400 m2/s2) will support the
risk for a few tornadoes and damaging wind gusts where the line can
stay near-surface based overnight. See the prior outlook for
additional information.
..Lyons.. 02/12/2025
.PREV DISCUSSION... /ISSUED 1044 AM CST Wed Feb 12 2025/
...Lower Mississippi Valley to Southeast States...
As a longwave trough amplifies over the Great Plains, strengthening
cyclonically influenced deep-layer southwesterly winds will
partially overlie an increasingly moist/unstable northward-shifting
warm sector today, with storms expected to steadily increase in
coverage and intensity through the afternoon especially across parts
of Louisiana/Mississippi into Alabama.
Early morning analysis features a northward-shifting maritime warm
front just inland from, and parallel to, the Gulf coast, with
near-70F surface dewpoints becoming increasingly common as of 9am
CST/15z from the upper Texas Coast to near the New Orleans Metro and
Alabama/Florida border vicinity. Similarly, even prior to the warm
front arrival, the KLIX 12z observed sounding sampled a 1.63 inch
Precipitable Water and 13.3 g/kg mean mixing ratio, which are in the
upper 5-10 percent of daily climo values, illustrating the quality
of near-coastal low-level moisture. While multi-layer cloud cover is
prevalent north of the warm front, more aggressive heating/isolation
is evident in proximity to the Gulf coast with deepening cumuliform
development within the warm sector. These trends in concert with
short-term guidance suggest that MLCAPE will exceed 1000 J/kg
especially across southeast Louisiana, the southern half of
Mississippi into southwest Alabama by mid/late afternoon.
Expect warm sector storm development to begin during the early
afternoon once convective inhibition erodes. Given the strength of
deep-layer shear and expected low-level curvature, some supercells
capable of all severe hazards, including tornadoes, are possible. A
few strong tornadoes are possible. In particular, short-term
guidance advertises a notable increase in southwesterly 850 winds
(lowest 1-2km AGL) by early evening (circa 00z) across
Mississippi/Alabama, which could enhance potential for supercell
sustenance and stronger tornado potential late this afternoon
through evening.
Another round of thunderstorms is anticipated during the evening and
overnight as the cold front accelerates east-southeastward across
the region. The strength of these storms could be modulated by the
coverage of the preceding afternoon storms, with greater storm
coverage reducing buoyancy. However, current expectation is that
persistent low-level theta-e advection will allow for airmass
recovery, and that strong to severe storms are likely within this
convective line. Primary severe risk with the line is damaging
gusts, but low-level shear will remain strong enough to also support
the potential for QLCS-related tornadoes as well.
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