Severe WX Severe Threat 17-18 March 2021

[Timhsv]

Those PDS soundings are widespread through northwest and west/central AL by midday Wednesday, with multiple sounding points in west AL showing SBCAPE a touch over 3000 j/kg.

Yes sir indeed. 3000 is just plain dangerous. I am beginning to feel that knot in my stomach to be seriously honest at this point.

 

[Casuarina Head]

I'm not really sure how climate change applies to this particular event-based thread. It most certainly shouldn't be used as reasoning when formulating a forecast or expectations for this event.

Indirectly, I think it holds some relevance. Climate change is leading to forces that make widespread, violent tornado activity—that is, outbreaks with multiple long-tracking supercell tornado families over a wide geographic area—less likely than it was prior to 1965 and especially prior to 2013. Certain models, including mesoscale such as the NAM/HRRR, still struggle to account for climate change’s impact on wavelengths vis-à-vis the warmer Pacific and the weaker AMOC signal in the Atlantic. Significant tornado outbreaks can still occur, but they are becoming less frequent, more limited in aerial coverage, and more confined to one (or two) big supercell that thrives more due to mesoscale quirks than large-scale synoptic factors vs. the past. Just a day and a half ago the GFS was suggesting a widespread SIGTOR threat from the Gulf Coast northward to IL/IN. Now the SIGTOR threat looks to be more confined, geographically, to parts of MS/AL and more dependent on boundaries than synoptic-scale factors, given that models have trended toward a higher-amplitude solution than a day and a half ago or so. Now we are still likely to see some significant tornadoes, but the potential “ceiling” does not look to be quite as menacing as it did earlier, though that can change.




Note the trend toward a higher-amplitude solution (left panel) due to a deeper trough over the Gulf of Alaska.

Old GFS run:

 

[JBishopwx]

SPC goes 30% or what will be an Enhance on Day 4 (Wednesday)

 

[Timhsv]

We now have a 30% SVR at DAY 4. We now have a distinct possibility of an outbreak of some magnitude at the moment.

 

[Fred Gossage]

That will be expanded through north AL and middle TN once the SPC finally realizes that the Euro is over-convecting like it has done a lot the past few years and the warm front is going to make it well into Tennessee...

 

[tennessee storm chaser]

That will be expanded through north AL and middle TN once the SPC finally realizes that the Euro is over-convecting like it has done a lot the past few years and the warm front is going to make it well into Tennessee...

 

[tennessee storm chaser]

That will be expanded through north AL and middle TN once the SPC finally realizes that the Euro is over-convecting like it has done a lot the past few years and the warm front is going to make it well into Tennessee...

How far north you see the warm front getting to Fred .? Your opinion

 

[Fred Gossage]

How far north you see the warm front getting to Fred .? Your opinion

Solidly to Nashville, at least.

 

[Timhsv]

That will be expanded through north AL and middle TN once the SPC finally realizes that the Euro is over-convecting like it has done a lot the past few years and the warm front is going to make it well into Tennessee...

Yes sir....

 

[tennessee storm chaser]

If the slower solution continues , the 30 percent zone will nudge even further north .

 

[Fred Gossage]

If the slower solution continues , the 30 percent zone will nudge even further north .

It's not timing that is causing that. It's that the Euro is showing more convection and keeping the warm front farther south. They're accounting for uncertainty. The Euro has done this with a lot of systems the last few years, and with the large scale EML to the southwest in the morning and anticyclonic flow aloft during the morning until nearly midday, convection shouldn't be that widespread. It's not a matter of timing.

 

[tennessee storm chaser]

It's not timing that is causing that. It's that the Euro is showing more convection and keeping the warm front farther south. They're accounting for uncertainty. The Euro has done this with a lot of systems the last few years, and with the large scale EML to the southwest in the morning and anticyclonic flow aloft during the morning until nearly midday, convection shouldn't be that widespread. It's not a matter of timing.

Makes a lot sense Fred , got you. Euro has been know for that . Could get very interesting say least for least southen portions Tennessee Wednesday afternoon

 

[Fred Gossage]

Makes a lot sense Fred , got you. Euro has been know for that . Could get very interesting say least for least southen portions Tennessee Wednesday afternoon

I think Dyersburg to Murfreesboro southward through Tennessee has a high probability of being in the warm sector of the secondary tropical warm front. There will be another warm front farther north over the Ohio Valley, and there could be tornadic storms between these two from northern Tennessee into the Ohio Valley. The highest threat of the long-trackers sets up near and south of that secondary maritime tropical warm front that will push north into west and middle Tennessee.

 

[tennessee storm chaser]

Dare I say. This system is starting give me some bad vibes of another system which happen to come on same day of the week. Course different type setup . But even me a chaser and lover of severe weather am getting few knots in my stomach even.

 

[Richardjacks]

Indirectly, I think it holds some relevance. Climate change is leading to forces that make widespread, violent tornado activity—that is, outbreaks with multiple long-tracking supercell tornado families over a wide geographic area—less likely than it was prior to 1965 and especially prior to 2013. Certain models, including mesoscale such as the NAM/HRRR, still struggle to account for climate change’s impact on wavelengths vis-à-vis the warmer Pacific and the weaker AMOC signal in the Atlantic. Significant tornado outbreaks can still occur, but they are becoming less frequent, more limited in aerial coverage, and more confined to one (or two) big supercell that thrives more due to mesoscale quirks than large-scale synoptic factors vs. the past. Just a day and a half ago the GFS was suggesting a widespread SIGTOR threat from the Gulf Coast northward to IL/IN. Now the SIGTOR threat looks to be more confined, geographically, to parts of MS/AL and more dependent on boundaries than synoptic-scale factors, given that models have trended toward a higher-amplitude solution than a day and a half ago or so. Now we are still likely to see some significant tornadoes, but the potential “ceiling” does not look to be quite as menacing as it did earlier, though.

Can I just say that tornado outbreaks are AlWAYS dependent on both synoptic AND mesoscale features. The synoptic setup could be perfect but that doesn't always guarantee a healthy EML, nor does it guarantee backing low level winds...thats just a couple of examples.

 

[Gail]

I hate days like this. My entire state (Mississippi) is under the gun. It’s spring break week so I’m worried about kids home alone. I wouldn’t be surprised if we end up at the school at some point on Wednesday (the cafeteria/gym is a tornado shelter).

 

[Brice Wood]

I’m very worried about this threat, this is tied or above the Easter Sunday outbreak and we all know what happened on that day

 

[warneagle]

The SPC also added a 15% area for Thursday, so I'll update the thread title to reflect that.

 

[Brice Wood]

The SPC also added a 15% area for Thursday, so I'll update the thread title to reflect that.

Alright, thanks for making this thread too!

 

[warneagle]

Alright, thanks for making this thread too!

No problem, it's not exactly labor intensive haha