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Severe WX Severe Threat 17-18 March 2021

Ingyball said:
Need to start watching the hourly HRRR now because the 2z run keeps things pretty discrete during the afternoon with some impressive soundings in Alabama. Much better hodos and helicity at 20z compared to the 0z run.
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Alan Gerard elaborated further on what you were talking about a moment ago.

 
Fred Gossage said:
I don't like to commit to phrases like that because of the way it gets interpreted in this post-4/27 world, but I will put it this way. If I was the SPC forecaster on desk tonight, I would be drawing a 6z Day 1 High Risk over the northern 2/3 of Mississippi and Alabama, northward into the Highway 64 counties of southern middle and southwestern Tennessee. A little bit of that is a similar situation to where a local WFO may put a winter storm warning out when they are still slightly uncertain about a true face value statistical verification, but they are doing it because of the conditional danger and from the public awareness standpoint, but the vast majority of the decision there comes from the thought process after taking the consensus of how the CAMs evolve a "baseline" scenario for this and then stepping back and looking at the actual meteorology of the setup outside of the CAMs, there is too much of a risk of multiple long-track EF3+ tornadoes to not go ahead and pull the trigger, imo.
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The SPC has been stingy with the "High" risks since the May 2019 TX/OK outbreak underperformed. Before that they had waited 2 years too. The SPC issued the PDS Tornado Watch the day of the Auburn/Opelika EF-4 but I guess they're afraid of crying wolf & things not get that bad.

In terms of what could happen, would the 24 April 2010 outbreak compare here @Fred Gossage ? That had 9 EF-2s, 4-3s & 2 4s.
 
darkskys25 said:
You beat me to it. Doesnt look messy to me at all. Perhaps he was talking about the line itself. I did see that it looked more linear and less broken on a recent run shown on abc3340. I guess they use barron?
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They do use Baron at ABC 33/40. The 00z high res models, at 100% pure face value, are a bit messy. They, for the most part, aren't clean 4/27 type supercells. Despite this, each solution still evolves with multiple violent caliber UH tracks.
 
brianc33710 said:
The SPC has been stingy with the "High" risks since the May 2019 TX/OK outbreak underperformed. Before that they had waited 2 years too. The SPC issued the PDS Tornado Watch the day of the Auburn/Opelika EF-4 but I guess they're afraid of crying wolf & things not get that bad.

In terms of what could happen, would the 24 April 2010 outbreak compare here @Fred Gossage ? That had 9 EF-2s, 4-3s & 2 4s.
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That day has actually been a synoptic analog for the setup.
 
Fred Gossage said:
They do use Baron at ABC 33/40. The 00z high res models, at 100% pure face value, are a bit messy. They, for the most part, aren't clean 4/27 type supercells. Despite this, each solution still evolves with multiple violent caliber UH tracks.
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Exactly. The UH output was pretty impressive regardless of the linear look. But the prefrontal cells were also showing uh tracks.
 
I'm surprised to see so much uncertainty at this stage of the game. Just a matter of time before people start calling Forecasted Convective Amplification Deficiency.
 
AL_ham_op said:
I'm surprised to see so much uncertainty at this stage of the game. Just a matter of time before people start calling Forecasted Convective Amplification Deficiency.
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The way it works these days, especially on social media, you could hand them a 1974/2011/1932 hybrid on a silver platter, and they would still do that.
 
There's been a shift in the HRRR once we got past the 00z run, and it's like a switch got flipped. This is the third consecutive run with a more progressive warm front, a more pristine EML that advects in at midday, and cleaner-looking mid-afternoon warm sector cells.
 
AL_ham_op said:
I'm surprised to see so much uncertainty at this stage of the game. Just a matter of time before people start calling Forecasted Convective Amplification Deficiency.
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There is always a degree of uncertainty. I see no reason to call a Forecasted Convective Amplification Deficiency. If anything the hrrr is pretty concerning as the storms in the afternoon look robust and i know we are primarly looking at the qlcs with embedded super cells or a broken line but the afternoon storms ahead of that line may bring a surprise.
 
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Instead of raw deterministic stuff, the SPC rightfully makes a lot of decisions on ensemble type output like this, since it weighs multiple outcomes together with and against each other and is statistical/probabilistically based. That very well could possibly get them to not only pull the trigger on a HIGH but as far north as southern middle TN and the HSV metro area.
 
Fred Gossage said:
There's been a shift in the HRRR once we got past the 00z run, and it's like a switch got flipped. This is the third consecutive run with a more progressive warm front, a more pristine EML that advects in at midday, and cleaner-looking mid-afternoon warm sector cells.
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was just looking at that. I will be surprised if i don't wake up to a high risk. Wow.

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I hope this doesn’t comes across as total noob....but I keep wondering about the CAD. I have looked at the temp and DP differences in N and NE AL vs NE MS, NW AL and central AL. Right now it is a chilly 53 in Guntersville with a DP of 52. The temps and DP in the western part of the state are 10-15 degrees warmer. The reason I keep focusing on the CAD is due to several instances where the CAD hung on tougher than the models had forecasted. I’m not good with historical dates and maybe someone can remember them for me. One instance was where the setup was somewhat similar- the warm front was forecasted to move into middle TN. Instead the warm front stalled around a line from NW AL through Birmingham and down through east central AL. That might have been the day of the Leesburg tornado (or maybe that was Beauregard in Lee County) (?). Another time was very similar, warm front never made it north of Marion county-Cullman-Boaz and that might have been either the Boaz or the Jacksonville tornado (?) But in any case, I’ve seen many forecasts for higher end days not verify for the N and NE part of the state due to the CAD and messy convection. Could we possibly stay at a moderate risk because of those questions? (Again, apologies if I didn’t use correct terminology due to noobism)
 
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Fred Gossage said:
If you don't follow us already, stay with us at the Tennessee Valley Weather Channel tomorrow. You can find us on Facebook by the link in my signature, on our website at tnvalleyweather.com, on YouTube by searching for Tennessee Valley Weather, and you can download our free app by searching for Tennessee Valley Weather in your app store. We are based out of Lawrenceburg at WLX Radio, and we provide a local focus on northwest Alabama, southern Tennessee, and northeast Mississippi. We will provide live non-stop team coverage tomorrow and tomorrow night for any tornado warnings in the area.
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Thank you thank you thank you!!!
 
On the one hand I'd say the strong advection with such a dynamic system should have no problem lifting the warm front and clearing out the CAD in time for the show, but modeling still having some disagreement at this short a range makes things a little less than fully certain; the HRRR seems a little too messy in the warm sector on some of the recent runs, so really we might need to get into obs range before we have a 100% lock on what's going on with at least the afternoon round. Nevertheless with these parameters every shower and radar blip is going to want to rotate so I won't be trusting any convection that occurs...
 
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