re: Multi-day Severe Weather Threat: 3/23-3/24

The most recent SPC update sounds way better. They’ve backed off on the potential for large long track tornadoes though there still is some potential for them.


Lower MS Valley, Mid-South, and the TN Valley...
Thunderstorms are ongoing along a baroclinic zone from KY southwest
to the Edwards Plateau in central TX. Composite outflow has
effectively shunted the surface front southeastward this morning.
Most CAMs that reasonably handled this convection suggest the recent
weakening trend will continue through late morning before renewed
storm development occurs towards early afternoon in the OK/TX/AR
border vicinity near the primary surface cyclone. This latter
activity should drive the broader coverage portion of the severe
threat as the surface cyclone deepens and tracks northeast along the
baroclinic zone through tonight. Reliable CAM guidance is largely in
agreement that an intensifying QLCS will evolve across AR and spread
towards the TN Valley through the evening. Here, strengthening
low-level winds and enlarging hodographs should compensate for the
northern gradient of the surface-based instability plume. This QLCS
will likely contain embedded supercell and mesovortex structures
supportive of tornadoes (including potential for a few EF2s) and
significant damaging wind swaths (up to around 90 mph).

Farther south, GOES PW imagery and the 12Z LCH/LIX soundings
indicate values have fallen to near an 1 inch along the central Gulf
Coast. This dryness pocket above 850 mb will limit buoyancy across
the Lower MS Valley until late today. Increasing low-level moisture
across the Sabine Valley towards the Ark-La-Miss should eventually
yield a plume of moderate MLCAPE around 1500 J/kg by evening. This
warm theta-e advection regime should also foster some discrete
convection ahead/southeast of the QLCS towards late afternoon into
early evening within the resultant MLCAPE gradient. Deep-layer shear
profiles will support supercells, a few of which could become
long-tracked. Low-level hodographs, while not quite as enlarged as
compared to farther north, will favor a threat for strong tornadoes
(EF2-3), until warm sector winds becomes increasingly veered from
southwest to northeast overnight.

Can’t wait for all the bitching about school closures when it ends up a bust

The NAM is pretty anemic with the pre-frontal storms and line farther south. HRRR is still pushing significant development. But, NAM shows a pretty potent environment with just about every sounding being a PDS. I don't necessarily buy the weak look of the NAM with it just developing nothing. Still, looks like the best environment is across northern LA into west central MS.

FWIW, the NAM is well off of current temps by 3-6° across the warm sector.

The saving grace by be dry air aloft which is evident on observed soundings, but that's usually a tough bet with southeast setups.

Thread is pretty quiet today surprisingly

We’ve mostly just had consistent rainfall starting last night. In a bit of a break right now.

Have a wind advisory for tomorrow though. Ugh.

Low 70s and cloudy all day here. Maybe that will keep a lid on things.

First warning of the day north of Texarkana

Latest SPC Update

SUMMARY...
A severe weather outbreak remains possible across the Lower
Mississippi Valley and Mid-South this afternoon and tonight, with
isolated large hail, scattered damaging/severe winds, and several
tornadoes expected. The most likely time period for strong tornadoes
is between 5 pm and Midnight CDT.

...20Z Update...
No changes have been made to the Moderate Risk area. Convection is
beginning to increase in coverage and intensity ahead of the cold
across far east TX, in addition to the ongoing activity along the
front itself. As a southerly low-level jet strengthens late this
afternoon into this evening, a corresponding increase in effective
SRH will likely lead to greater tornado potential with time. The
greatest threat for strong tornadoes remains apparent this evening
across parts of northern LA into southern/eastern AR,
northern/central MS, and western/middle TN. This will especially be
the case with any supercells that can remain discrete ahead of the
line.

A bowing line/MCS will likely develop this evening as convection
grows upscale along/ahead of the front. The northern extent of
appreciable severe threat will likely be constrained by a
convectively reinforced outflow boundary from thunderstorms earlier
today that currently extends from parts of AR into TN. This boundary
will attempt to lift back northward this evening and overnight as a
surface low deepens from the Mid-South into the lower OH Valley.
Still, the threat for damaging winds and tornadoes should become
increasingly limited with northward extent into KY and the OH
Valley.

Through April and early May for the deep south, I believe.