• Welcome to TalkWeather!
    We see you lurking around TalkWeather! Take the extra step and join us today to view attachments, see less ads and maybe even join the discussion.
    CLICK TO JOIN TALKWEATHER

Severe Weather Threat 4/28-4/30

UK_EF4 said:
I think the risk for a significant tornado event remains quite high, unfortunately.

Synoptics should always be the go-to, especially at D3/4 range. And for synoptics, things are in my opinion concerning. SREF indicates a pretty clean and rapid ejection of a negatively tilted shortwave through the broader positively tilted trough.

View attachment 40397

Chris Broyles' paper suggested fast moving jet streaks such as these can generate localized areas of strong vertical motion that can aid in producing long track tornadic supercells. That's why despite capping concerns, and the fact a fair few models show little in the way of precipitation, I'm not necessarily thinking lack of storms is the likely fail mode. You'd be hard pressed to find a jet streak like this impinging right on the northern end of rich moisture and not get storms. Models often struggle with initiation this range.

On the other side of things, you could make an argument with generally SW that rapid upscale growth is favored. Yet as the dryline and any potential pre-frontal confluence curves into the surface low, the angle between them is reasonably large and would support at least a reasonably long window of semi-discrete or discrete storm mode. Especially if your CIN and mid level dry air are on the stronger side these things may strike a balance. Will have to keep an eye on CAMs though for hints on what the convective evolution may be like.

View attachment 40398

The environment remains exceptionally supportive, however, of strong, and potentially violent tornadoes, from about 20/21z onwards. Initially that will be thermodynamically driven, but kinematics become highly favorable from 22-00z onwards.

View attachment 40399

That risk obviously hinges on whether we do actually get robust supercells. My early guess now is we get at least 1-2 robust storms. Whether we see that number increase probably dictates whether we move more towards a High-Risk scenario, and depends on how the trough ejection, capping, and any boundaries influence storm initiation and mode.

The main failure mode I'm watching for now is whether the trough ejection is too fast. Obviously, having a faster trough ejection increases the severe risk, but in this case when its already very fast (40kts+), any faster and the best upper level support which would favor discrete supercells will outrun the EF3+ parameter space and things may be somewhat moderated. We've seen hints of this, particularly on the NAM, though the historical bias suggests models can be a tad fast at this range. So will need watching.

Long story short, Monday looks potentially volatile. I think D3 MDT was the right call, but we will have to see how the forecast progresses.
Click to expand...

Thanks always oh great forecaster @UK_EF4
 
UK_EF4 said:
I think the risk for a significant tornado event remains quite high, unfortunately.

Synoptics should always be the go-to, especially at D3/4 range. And for synoptics, things are in my opinion concerning. SREF indicates a pretty clean and rapid ejection of a negatively tilted shortwave through the broader positively tilted trough.

View attachment 40397

Chris Broyles' paper suggested fast moving jet streaks such as these can generate localized areas of strong vertical motion that can aid in producing long track tornadic supercells. That's why despite capping concerns, and the fact a fair few models show little in the way of precipitation, I'm not necessarily thinking lack of storms is the likely fail mode. You'd be hard pressed to find a jet streak like this impinging right on the northern end of rich moisture and not get storms. Models often struggle with initiation this range.

On the other side of things, you could make an argument with generally SW that rapid upscale growth is favored. Yet as the dryline and any potential pre-frontal confluence curves into the surface low, the angle between them is reasonably large and would support at least a reasonably long window of semi-discrete or discrete storm mode. Especially if your CIN and mid level dry air are on the stronger side these things may strike a balance. Will have to keep an eye on CAMs though for hints on what the convective evolution may be like.

View attachment 40398

The environment remains exceptionally supportive, however, of strong, and potentially violent tornadoes, from about 20/21z onwards. Initially that will be thermodynamically driven, but kinematics become highly favorable from 22-00z onwards.

View attachment 40399

That risk obviously hinges on whether we do actually get robust supercells. My early guess now is we get at least 1-2 robust storms. Whether we see that number increase probably dictates whether we move more towards a High-Risk scenario, and depends on how the trough ejection, capping, and any boundaries influence storm initiation and mode.

The main failure mode I'm watching for now is whether the trough ejection is too fast. Obviously, having a faster trough ejection increases the severe risk, but in this case when its already very fast (40kts+), any faster and the best upper level support which would favor discrete supercells will outrun the EF3+ parameter space and things may be somewhat moderated. We've seen hints of this, particularly on the NAM, though the historical bias suggests models can be a tad fast at this range. So will need watching.

Long story short, Monday looks potentially volatile. I think D3 MDT was the right call, but we will have to see how the forecast progresses.
Click to expand...
Great write up, thank you!!
 
US_Highway15 said:
Yes. Not saying this will happen, but one of the things that made Palm Sunday 1965 so violent, is the fact that the setup had decent capping in place throughout the day that made the storm mode discrete, and kept any other potential convection from developing, messing up the setup.
Click to expand...
Capping is very important to limit crapvection and from storms going too early until the right time, like you noted. The main factors in storm mode comes down to forcing (is it subtle or strong) and deep layer shear vector orientation with respect to the initiating boundary.

One thing I wasn’t aware of on Palm Sunday was that the cold front (the main forcing mechanism) was actually more of a pacific-front or Psuedo-cold front/dryline. The difference of the temperature gradients on each side of it was very small, and because of that, forcing was very subtle. In a more traditional synoptic cold front, the stronger forcing just forces a ton of storms to go up in a line.

I will say, i feel like plains events are traditionally more “aesthetic” on radar and in action than Dixie alley events because you’ll get 3-4 storms in the plains because of that dry line. Unlike Dixie, where you will get an absolute huge rain shield with 2-3 supercells trying to compete and outrun the cold front and the additional crapvection all around them.
 
Schoeppeya said:
HRRR depicting a very high end environment at 0z Monday night. Wowza

ETA:. This is a crazy sounding forecast near the iowa/minnesota border. Cape >3k, 0-3km SRH>500, LCL's under 300, and 3Cape of 189 is nuts.
View attachment 40404
Click to expand...
If this were to verify, multiple long tacked, intense to violent tornadoes could occur. potentially two or more on the ground at once...


Don't let Broyles see this-
 
Also, hot take but people are reading WAY too much into the 0Z HRRR run. I mean its a reading from 36 hours out. Its just barely cracking Monday's potential outbreak. I think 06Z or 12Z should be the runs where we really take it into consideration.
 
You must log in or register to reply here.
Back
Top