Let's Do It Again: Severe Threat 3/30 - Line of Severe Storms leaving SELA. AL in it now

It's the heart of severe season and we got another round coming middle of the week.

The main story will be Wednesday, as an intense wind event should unfold over Louisiana, Mississippi, and Alabama. There will be strong winds ahead of a vigorous line of thunderstorms, with gusts over 40 mph expected and some locations getting 50+ mph gusts without any storms. Where the sun comes out and allows enough heating for the boundary layer to mix will have the highest gust potential.

Within the line, strong winds aloft will get pulled into the line and brought to the surface creating the potential for widespread damaging winds within bowing segments. There will also likely be short lived tornadoes imbedded within the line, some of which could be intense.

The highest risk of this will be north of I12 but most of Louisiana still has a decent risk of damaging straight line winds.

Also, I hope this thread leads to numerous minor inconveniences for WaWaWeeWa. Not sure how it would, but I still hope it does.

SPC Outlook:

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A band of convection, with embedded strong/locally severe
thunderstorms, is ongoing from the west-central Ozarks to northeast
TX. See SPC tornado watch 75 and related mesoscale discussions for
near-term guidance on associated severe potential.

As the basal shortwave trough pivots out today, strong height falls
and rapidly increasing low/middle-level wind fields will spread
farther over the warm sector adjacent to the ongoing, eastward-
shifting convective band. In keeping with that mass response and
the geometry of the height/vorticity fields, the convective band
should pivot toward a more meridional alignment as well.
Strengthening of both deep ascent and low-level moisture/theta-e
will reduce MLCINH observed in this morning's 06Z and 12Z
warm-sector soundings, contributing to increasing intensity and
coverage of thunderstorms in the main band, as well as some
potential for convection to develop to its east. How much sustained
convection can form ahead of the line will strongly influence the
tornado threat, which will be strong with the main line, but which
will be especially intense for any sustained supercells that can
form to its east.

The most-favorable parameter space still appears to be across the
"moderate" area, where the greatest wind and tornado probabilities
are drawn (including at least 10% significant-severe levels). In a
northward-narrowing wedge of favorable warm-sector boundary layer,
mid/upper 60s F surface dew points should become common from the
Gulf Coast to parts of the Mid-South, decreasing northward to the
mid 50s to low 60s south of the warm front, over outlooked parts of
IL/IN. Though diurnal heating will be modest over most of the area,
a combination of theta-e advection and cooling aloft will contribute
to MLCAPE ranging from 500-1500 J/kg over parts of LA/MS/AL mainly
south of I-20, decreasing to the 100-500 J/kg range near the Ohio
Valley.

Shear will be strong across the entire region, as 90-110 kt of
700-500-mb layer flow develop ahead of the ejecting shortwave trough
over the Mid-South, along with a broad, 60-85-kt LLJ. Forecast
soundings reasonably depict 50-70 kt effective-shear magnitudes,
along with large, well-curved hodographs fostering 300-600 J/kg
effective SRH (locally higher). This will support line-embedded
tornadic supercells and LEWP/mesovortex features, as well as bowing
segments to locally maximize destructive-wind potential. Any
preceding, sustained supercells that do develop would be fast-moving
(around 50 kt based on the Bunkers algorithm), with potential for
long tornado tracks if storm-scale occlusions are not very rapid.
Downward momentum transfer from layers of intense gradient flow in
low/middle-levels also my augment the severe-downdraft threat, with
bursts of hurricane-force gusts possible.

The convective regime should weaken with time and eastern extent
this evening and overnight across the Ohio Valley region, but may
persist at severe levels through the night across the Gulf Coastal
Plain as far east as eastern/southern AL, western GA and the FL
Panhandle, where sporadic severe gusts and at least a few tornadoes
will remain possible overnight

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Wednesday Damaging Wind and Tornado Threat

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An extensive risk for damaging winds exists across all of the Lower Mississippi Valley and eastward into western Alabama. The greatest risk will be in segments of the line that bow out. In addition, strong winds ahead of the line will be very noticeable tomorrow with potential to knock out power in some locations. Have a way to get warnings without power due to this potential. Those winds will have gusts into the 40 mph range but gusts above 50 and even up to 60 are not unreasonable ahead of any storms.

There is also a tornado threat for stronger than normal and longer last than normal tornadoes within the line of storms. Take those spin ups as seriously as you would a tornado ahead of the line. In addition, there is some concern of the line breaking along the southern extent of the storms, which also increases the threat of strong tornadoes if it were to materialize. While I have some concern in southern Louisiana for that scenario, I still think the most likely spot would be farther east along and to the east of I59. The powerful shear available means it doesn’t take much of an updraft to get spinning and developing.

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