Severe WX Severe Threat 17-18 March 2021

[warneagle]

Lotta red and purple on this map.. Anything over 1 is sufficient for tornadoes right?


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Here's an explainer from the SPC. tl;dr most sigtors occur in conditions with STP >1.

 

[jmills]

Oops! Yes, EHN sorry.

Hopefully things STAY at the ENH level, but even ENH is still something to watch.... CLOSELY.

And I will be up all night Wednesday watching this with my Wx radios charged, RadarScope on my phone, Twitter on my iPad, and my laptop on several weather pages (including IEMBot).

Thanks again Fred!

Highly doubt we stay at an ENH. I see a fairly large MOD coming day 2.

 

[Jpgood97]

Do we think this will go moderate risk at some point? What would be the limiting factor(s) to upgrade the risk?

 

[CheeselandSkies]

I've noticed that 05/04/03 is popping up as an analog on a lot of the NAM soundings...

Haven't really seen it on the analogs but another event that comes to mind from the general area under the gun is Super Tuesday '08...Arkansas, Memphis to Jackson (TN) area, and northern Alabama all had significant tornadoes.

 

[Equus]

I'd assume a moderate is locked in for D2 /D1 if trends continue, might wait til D1 but hard to say.

 

[CheeselandSkies]

Do we think this will go moderate risk at some point? What would be the limiting factor(s) to upgrade the risk?

At *least* moderate.

 

[Richardjacks]

The parameter space for this is ominous. Usually we get a fairly narrow corridor of favorable conditions but looks like this could be a longer duration event.

Overall that is one main difference that set this apart from other days. The parameters are not just impressive, but over a large area for an extended period of time, this creates the opportunity for nit just 1 or 2 quick violent tornaodes, but long-tracked multiple ones.

 

[Fred Gossage]

Do we think this will go moderate risk at some point? What would be the limiting factor(s) to upgrade the risk?

I think this gets a Day 2 Moderate Risk. The only two real question marks had been the low-level shear and warm frontal position. We've seen what everything is locking onto in regards to the low-level shear. The models are also seemingly locking onto blasting the warm front well up into middle Tennessee. And these trends on today's runs are important because the upper low is now fully onshore and in our upper-air network. It's being fully sampled by actual observations, and those observations are going into these model runs. There's always some inherent uncertainty, no matter what, but we are steadily trending toward working past the last remaining question marks.

 

[BraxBanksOKWX]

Do we think this will go moderate risk at some point? What would be the limiting factor(s) to upgrade the risk?

If the models continue to trend the way they are currently, a moderate risk is on the table for sure. Tonight some more high-resolution models will be in the range of Wednesday, so those will also play a factor I'd imagine. Could even see a Day 2 moderate risk.

 

[warneagle]

Do we think this will go moderate risk at some point? What would be the limiting factor(s) to upgrade the risk?

I think a Day 2 MDT is pretty likely given the recent trends in the models. The threshold for a Day 2 MDT for tornadoes is 15% w/sig severe, and that would definitely be justified unless the trend of the last couple of model runs reverses on the next couple of runs.

 

[warneagle]

Haven't really seen it on the analogs but another event that comes to mind from the general area under the gun is Super Tuesday '08...Arkansas, Memphis to Jackson (TN) area, and northern Alabama all had significant tornadoes.

05/04/03 also produced a violent tornado in the Jackson, TN area, incidentally. That event was focused further north and west (with violent tornadoes up into Kansas and Missouri) than Super Tuesday was, but it definitely caught my eye when it popped up on three or four soundings in a row. That was the biggest day of the extended May 2003 outbreak (85 tornadoes, four F4s).

 

[Justin Hindman]

I think a Day 2 MDT is pretty likely given the recent trends in the models. The threshold for a Day 2 MDT for tornadoes is 15% w/sig severe, and that would definitely be justified unless the trend of the last couple of model runs reverses on the next couple of runs.

A moderate is definitely warranted, however I’m not sure if they pull it on day 2. If they do it would be the noon update when things are a little more clear on smaller details. They have gone conservative on day 3/2 and sometimes even day 1 until they the lunch update on day one. In any case, it looks like a long day that will have to be monitored.

 

[KoD]

Is there a chance that portions of the warm front could see convection that limits the spacial extent of the threat area? Particularly in the northern areas?

I imagine if that was the case there's still a huge region potentially under the gun.

 

[Fred Gossage]

Is there a chance that portions of the warm front could see convection that limits the spacial extent of the threat area? Particularly in the northern areas?

I imagine if that was the case there's still a huge region potentially under the gun.

By leaps, bounds, and back handsprings, that is becoming less and less of a concern in north AL and even southern TN. Even the least bullish models blast the warm front deep up into middle TN now.

 

[Vols1]

So every model continues a northern trend Fred? Last night you said then it looked like it would clear southern middle Tennessee. Things changing? Nashville more in play?

 

[Fred Gossage]

A moderate is definitely warranted, however I’m not sure if they pull it on day 2. If they do it would be the noon update when things are a little more clear on smaller details. They have gone conservative on day 3/2 and sometimes even day 1 until they the lunch update on day one. In any case, it looks like a long day that will have to be monitored.

This isn't like the past significant tornado setups we've had over the past several years. This isn't the type of event where there might be a strong tornado or two if small-scale details come together at the last minute. This is glaringly obvious. Helen Keller could see that this is a synoptically-driven violent tornado event (I'm very close to using the word "outbreak" in our public products, and I cringe at the idea of doing that). This is the type of setup where most of the smaller-scale details we often watch for at the last minute are gonna be molded by the synoptic-scale features. This is, of course, nowhere close to a 4/27/11, by any remote stretch, but this is easily a more serious threat to the area than 4/28/14 ever thought of being, and that was the most serious threat to the area since 4/27.

If an upgrade to MDT is not placed on the map tonight, unless something radically changes from even what the least bullish models suggest, it's a horrible disservice to the forecast process with this thing.

 

[Fred Gossage]

So every model continues a northern trend Fred? Last night you said then it looked like it would clear southern middle Tennessee. Things changing? Nashville more in play?

The steady trend across the board is that may be the case. I think we're at least talking as far north as all of Hickman and Maury, but we may be talking about straight up to I-40 or even a hair north.

 

[tennessee storm chaser]

05/04/03 also produced a violent tornado in the Jackson, TN area, incidentally. That event was focused further north and west (with violent tornadoes up into Kansas and Missouri) than Super Tuesday was, but it definitely caught my eye when it popped up on three or four soundings in a row. That was the biggest day of the extended May 2003 outbreak (85 tornadoes, four F4s).

12z NAM is even stronger with the 850mb jet. We're now talking about a 67 to almost 70 kt max and a much bigger area of 60+ evening and overnight. It's also trending stronger with the 850mb winds during peak heating as well.

i live in Jackson tennessee, remember that night well
M

 

[Vols1]

Ok. If your on the front or 10-20 miles north does that make a huge difference or can the storm kinda keep on going just lose some of its punch

 

[Fred Gossage]

Ok. If your on the front or 10-20 miles north does that make a huge difference or can the storm kinda keep on going just lose some of its punch

The dynamics are strong enough that a supercell crossing the front could go for a few tens of miles with a significant tornado than it usually would be able to in most other events. These aren't the details you need to get caught up in right now. You were in a tornado risk prior to these new trends. Be aware and prepared regardless.