Severe WX Severe Weather Threat 4/5/17-4/6/17

Richardjacks said:
if you use the idea of that if there is any uncertainty, than you should not post a high risk, then no. however, I don't know of any weather event where there wasn't at least some uncertainty.
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So basically it could go either way?
 
Yesterday's event outpreformed the severe thunderstorm watch they posted in GA.... If they're feeling any political kickback from that, I wouldn't be surprised for them to err on the side of caution and go ahead and post a worst case outlook to get the word out.
 
I am curious, does anyone else see somewhat of a disconnect between the best instability and shear for tomorrow? For example, on the 12Z 3KM NAM valid for 21Z tomorrow, you have SBCAPES of 3-4K over much of central and southern Alabama. Yet 0-1KM SRH is mostly <200m2/s2 in that area. The higher values are displaced to the east over GA where there is no CAPE progged.

I can't get any soundings to pull up on Pivotal Weather, but on earlier runs I saw a lot of the critical angles in the hodographs were around 40-50 degrees, rather than the 90-ish degrees you look for for classic significant tornado setups.

I'm thinking the reasoning for this is the progged location of the surface low, to the NNW, thus the cold front is oriented NE-SW with veered low level winds along it. Normally you would expect with a deepening surface low to the NW you would have strong and backing low-level winds out ahead of the triple point, into the warm sector, and correspondingly high SRH.

Any thoughts as to whether the parameters may end up lining up better than shown verbatim, or if this is accurate could this be a caveat putting a ceiling on long-track strong-violent tornado potential? Could be one of those scenarios where tornado potential is limited except perhaps where a boundary left by the morning storms locally enhances SRH?

Not saying this will null the event's potential...just another uncertainty/ceiling factor to watch for?
 
Okay I just got a chance to look at the NMM and yeah...wow. If those thermos verify it's going to to be a long day.
 
Still a MDT risk on the new Day 2 Outlook, but the risk area was expanded slightly to the west:

swody2_categorical.png
 
Mentioned in the new outlook discussion they are saying they may need to upgrade the risk across TN and OH
 
Just as a point of reference, the area covered by the MDT risk in this morning's Day 2 Outlook was 59,931 sq mi. The area covered in the new outlook by the MDT risk is 96,371 sq mi.
 
Just... wow. Also Hailey your screenshot is still this morning's.
day2probotlk_1730_any.gif
 

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So much depends on the evolution of the morning convection, especially in northern Georgia. This event has a very high ceiling here, but also a moderately low floor if convection keeps training through the morning into the afternoon. Big boom or Forecasted Convective Amplification Deficiency potential in my opinion for n GA.
 
bs0500.conus.png
 
ARCC said:
The new WRFs

The ARW tempers the threat a little from 0z. Still serious but it wants to keep cape down. With lots of convection except for Central GA which gets nailed.

The NMM on the other hand goes absolutely bonkers. Backs wind direction at both the surface and 850mb ahead of the dry line and blows up several very long track supercells from west AL/central TN and marches them east. Is it wrong to say that we should use this model because it puts a very strong/long track supercell over the F5 capital of the world?

No doubt you would need a western and northern expansion of the higher a risk areas there.
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Not sure why but the NMM convective product almost always trends towards a worse case scenario.
 
CheeselandSkies said:
I am curious, does anyone else see somewhat of a disconnect between the best instability and shear for tomorrow? For example, on the 12Z 3KM NAM valid for 21Z tomorrow, you have SBCAPES of 3-4K over much of central and southern Alabama. Yet 0-1KM SRH is mostly <200m2/s2 in that area. The higher values are displaced to the east over GA where there is no CAPE progged.

I can't get any soundings to pull up on Pivotal Weather, but on earlier runs I saw a lot of the critical angles in the hodographs were around 40-50 degrees, rather than the 90-ish degrees you look for for classic significant tornado setups.

I'm thinking the reasoning for this is the progged location of the surface low, to the NNW, thus the cold front is oriented NE-SW with veered low level winds along it. Normally you would expect with a deepening surface low to the NW you would have strong and backing low-level winds out ahead of the triple point, into the warm sector, and correspondingly high SRH.

Any thoughts as to whether the parameters may end up lining up better than shown verbatim, or if this is accurate could this be a caveat putting a ceiling on long-track strong-violent tornado potential? Could be one of those scenarios where tornado potential is limited except perhaps where a boundary left by the morning storms locally enhances SRH?

Not saying this will null the event's potential...just another uncertainty/ceiling factor to watch for?
Click to expand...


No you are correct and it's been a part of the discussion for days. The thing is when you have explosive instability it can counter act low helicity, just as very high helicity can counter act low cape in winter time systems. In this environment 200-300 helicity is plenty to put down long track tornadoes.

Another thing is some of the models may be veering the winds too much. Don't be surprised to see the winds back toward the dry line.
 
KoD said:
Not sure why but the NMM convective product almost always trends towards a worse case scenario.
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They have always done that. It seems like the ARW takes the weak side and the NMM takes the strong. Even if you blend the two that is a very nasty look.
 
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