Severe WX Severe Threat 17-18 March 2021

[Timhsv]

 

[brianc33710]

Tornado driven D2 moderate risk on the first outlook... here we go

View attachment 6950

When was the last Moderate risk?

 

[Equus]

We had one in Texas on Saturday, but for this area I think April 19 last year?

 

[OHWX97]

Alabamians can't catch a break. So much of the state under that MDT risk.

 

[brianc33710]

SPC AC 160608

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0108 AM CDT Tue Mar 16 2021

Valid 171200Z - 181200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM
EAST-CENTRAL ARKANSAS AND SOUTHWESTERN TENNESSEE INTO NORTHERN AND
EASTERN MISSISSIPPI AND MUCH OF ARKANSAS...

...SUMMARY...
A broad area of substantial severe weather potential -- including
risk for large hail, damaging winds, and several strong tornadoes --
is anticipated Wednesday from the Arkansas/Louisiana vicinity
eastward across the central Gulf Coast states/southern Appalachians.

...Synopsis...
A compact/vigorous upper low initially over the Oklahoma area is
forecast to move steadily eastward through the period, spreading
strong flow aloft and a broad zone of enhanced ascent across the
south-central and into the southeastern CONUS. This low will reach
the Ozarks overnight, flanked by ridging across the Rockies, and
along the East Coast.

At the surface, a 998 mb low is progged to advance eastward along a
similar track, crossing northern Oklahoma/southern Kansas through
the day, and then the Ozarks overnight. A trailing cold front will
shift from eastern portions of the southern Plains and across
Arkansas/Louisiana through the afternoon, and then across the
Tennessee Valely and central Gulf Coast states through the end of
the period. Meanwhile, a warm front extending eastward from the low
across northern Arkansas/southern Missouri and then
east-southeastward across the Tennessee Valley into Georgia will
linger in place on its eastern fringe, but will lift slowly
northward in advance of the progressing low. These two fronts will
outline a broad/moist warm sector, which will gradually destabilize
through the day supporting a widespread/potentially significant
severe weather event.

...Southern MO/AR/LA vicinity east to the TN valley/western GA...
Scattered showers and thunderstorms are forecast to be ongoing ahead
of the cold front from eastern Oklahoma/western Arkansas southward
into east Texas, and east-southeastward along the warm front across
the Tennessee Valley area to the southern Appalachians.

As the synoptic system advances, convection over the central Gulf
Coast region/Southeast should remain generally north of the warm
front, while some decrease in pre-cold-frontal convection is also
expected through the morning. This should permit some heating of
the moist (generally mid 60s dewpoints) warm-sector boundary layer,
pushing mixed-layer CAPE values into the 1000 to 2000 J/kg range by
early afternoon.

New storm development is expected to occur from the southwestern
Missouri vicinity southward across the Arklatex region by early
afternoon. Strong shear -- including veering of the wind field with
height from southerly to southwesterly -- will support ready
evolution of rotating updrafts, with some long-lived storms likely
evolving with time. Along with large hail potential, locally
damaging winds will be possible, along with a steadily increasing
tornado risk through the afternoon. As storms move into central and
eastern Arkansas, at least a few intense supercells are expected,
within the broader area of storms. Potential for a couple of
significant tornadoes is apparent, with this risk spreading into
southwestern Tennessee and northern Mississippi with either
pre-cold-frontal storms moving eastward into the region, or with
other cells developing in a zone of increasing low-level warm
advection in the warm sector/near the warm front.

During the evening and into the overnight hours, substantial
strengthening of the low-level southerlies across the central Gulf
Coast region is expected. While some diurnal decrease in
instability is expected, this should be more than offset by the
increasing low-level and deep-layer shear. As such, risk for
additional/significant tornadoes is anticipated to last through the
overnight hours, focused particularly across much of Alabama. Hail
and relatively widespread damaging winds will also be possible
across this same region.

..Goss.. 03/16/2021

CLICK TO GET WUUS02 PTSDY2 PRODUCT

NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
CURRENT UTC TIME: 0633Z (1:33AM), RELOAD THIS PAGE TO UPDATE THE TIME

 

[RollTide18]

We had one in Texas on Saturday, but for this area I think April 19 last year?

For this area, yeah, April 19th. I remember distinctly because there was a twitter rumor that the SPC was going to go High Risk that day but they didn’t.

 

[Equus]

Wednesday is not going to be a fun day, giving me 4/24/10 vibes with the potential for wave after wave of supercells. Big sinking feeling that bad things are about to happen.

 

[Fred Gossage]

Looking over the evening/overnight run of the Baron 3k model that we get through our Lynx system. It has a cellular swarm starting 5-6pm over north-central MS/AL (MS/west TN/AR/LA stuff prior) with supercells as east as Clay County AL by 6pm... with a late-night "final line" coming through. The "final line" is woefully not a line, but is a band of spaced, fully discrete supercells with black to white reflectivity cores. The model has a full-on swarm of medium-range or stronger UH streaks through the warm sector, with several of them over MS/AL/far southern TN being near the top or at the top of the intensity scale. The 3k Baron, given the background environment, depicts a full-on open warm sector swarm with multiple violent long-tracked tornadoes possible.

 

[OHWX97]

Certainly worth mentioning that there's an enhanced risk for much of Georgie, South and North Caroline on Thursday. SPC outlook states the potential for all hazards of severe weather, including "several tornadoes - a couple of them possibly strong."

 

[CheeselandSkies]

Looking over the evening/overnight run of the Baron 3k model that we get through our Lynx system. It has a cellular swarm starting 5-6pm over north-central MS/AL (MS/west TN/AR/LA stuff prior) with supercells as east as Clay County AL by 6pm... with a late-night "final line" coming through. The "final line" is woefully not a line, but is a band of spaced, fully discrete supercells with black to white reflectivity cores. The model has a full-on swarm of medium-range or stronger UH streaks through the warm sector, with several of them over MS/AL/far southern TN being near the top or at the top of the intensity scale. The 3k Baron, given the background environment, depicts a full-on open warm sector swarm with multiple violent long-tracked tornadoes possible.

The NAM currently paints the most ominous environments over SW TN (where 3KM EHI values reach 6.5 at 21Z Wednesday) and the southern MS/AL border region.

 

[Fred Gossage]

Looking over the evening/overnight run of the Baron 3k model that we get through our Lynx system. It has a cellular swarm starting 5-6pm over north-central MS/AL (MS/west TN/AR/LA stuff prior) with supercells as east as Clay County AL by 6pm... with a late-night "final line" coming through. The "final line" is woefully not a line, but is a band of spaced, fully discrete supercells with black to white reflectivity cores. The model has a full-on swarm of medium-range or stronger UH streaks through the warm sector, with several of them over MS/AL/far southern TN being near the top or at the top of the intensity scale. The 3k Baron, given the background environment, depicts a full-on open warm sector swarm with multiple violent long-tracked tornadoes possible.

Given what we know about the background kinematics and forcing geometry and the parameter space, the Baron 3k is something of a caliber that I would be comfortable calling on air a "violent tornado outbreak".

 

[Keldeo]

Checking in from Little Rock. Nobody is really talking about us. I feel our threat here is going highly depend on when and where exactly convective initiation happens. We can get out unscathed if it gets delayed long enough. However if it happens on time or sooner then it can get ugly

 

[Fred Gossage]

Checking in from Little Rock. Nobody is really talking about us. I feel our threat here is going highly depend on when and where exactly convective initiation happens. We can get out unscathed if it gets delayed long enough. However if it happens on time or sooner then it can get ugly

Your threat is definitely more conditional and based on how convection plays out like you talked about. However, you are on the west end but included in the significant tornado risk if the more bullish solution pans out. Definitely be fully on guard.

 

[Fred Gossage]

NWS Birmingham has gone 5/5 on their confidence level for tornadoes Wednesday into Wednesday night. Since they started that HWO map there a good bit over a decade ago, I can count on one hand how many times they've done that.

 

[Clancy]

After taking a look at the models (albeit half awake), definitely looks concerning for all of Alabama. Still struggling to gauge the threat over here near Atlanta but definitely won't be fooling around with it. 06Z HRRR had some nasty looking discrete stuff drifting our way during the late afternoon into evening.

 

[tennessee storm chaser]

Checking in from Little Rock. Nobody is really talking about us. I feel our threat here is going highly depend on when and where exactly convective initiation happens. We can get out unscathed if it gets delayed long enough. However if it happens on time or sooner then it can get ugly

Klzk out Little Rock seems concerned with long track tornadoes

 

[Casuarina Head]

The 06Z GFS looks to have come in with the mid-level trough being more positively oriented around 18Z Wednesday afternoon, partly related to a more pronounced shortwave impulse over Lake Superior. The northern stream is also a bit faster on this run vs. yesterday’s 18Z. On the other hand, the background flow looks to be lower-amplitude vs. the 18Z run. The trend is definitely slower and lower-amplitude over time, which would maximise the northward expansion of the warm sector into TN and possibly eastern AR as well as extreme southwestern KY. This definitely doesn’t look good for MS/AL and increases the risk of strong/violent tornadoes over a wider area, possibly into GA as well. I definitely think that the ceiling of this event continues to rise as we move closer in time.

 

[tennessee storm chaser]

The 06Z GFS looks to have come in with the mid-level trough being more positively oriented around 18Z Wednesday afternoon, partly related to a more pronounced shortwave impulse over Lake Superior. The northern stream is also a bit faster on this run vs. yesterday’s 18Z. On the other hand, the background flow looks to be lower-amplitude vs. the 18Z run. The trend is definitely slower and lower-amplitude over time, which would maximise the northward expansion of the warm sector into TN and possibly eastern AR/extreme southwestern KY. This definitely doesn’t look good for MS/AL and increases the risk of strong/violent tornadoes over a wider area, possibly into GA as well.

So thinking good chance more west tennessee needs watch for discrete cells now...trying get a good idea how north warm front gets

 

[Fred Gossage]

So thinking good chance more west tennessee needs watch for discrete cells now...trying get a good idea how north warm front gets

I think anywhere along and south/west of a line from Paris, TN to Shelbyville, TN has at least a mid-range threat of a few long-tracked tornadoes. The deeper you get back into the area roughly south of the Highway 412 corridor in middle TN or west of Highway 641 in western TN... and then back down through MS/AL, the higher and more widespread that threat is.

 

[tennessee storm chaser]

What has me concerned is fact somewhere along that warm frontal boundary usually has a significant tornado riding along the boundary . Front seems get bout 75 to 100miles north of me