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Severe WX Severe Weather Threat 3/14-3/16

I want to people to keep in mind that what Nixon is saying isn’t one of those big red flag failure modes that slip under the nose and cause a massive Forecasted Convective Amplification Deficiency.

He’s simply highlighting minor monkey wrenches that could prevent Saturday from being a worse case scenario. In which, even the floor would still be devastating.

A day 3 moderate is in every way warranted for this event. It’s simply not possible for a SVR weather threat to not have failure modes, even April 27, 2011 had several.

It’s really just a matter of waiting and watching what the atmosphere does up until that point.
 
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andyhb said:
I'll touch on it. I think there's a little too much "applying Plains logic to the SE" going on here. Low LCLs are commonly concurrent with weak low level lapse rates. Temps need to warm at the surface to steepen low level lapse rates. By definition, if the dewpoint is not rising, this will increase T/Td spreads and lead to LCLs being higher. Should there be some degree of clearing on Saturday, there will be some heating.

Weak low level lapse rates are generally hostile to developing updrafts. With that said, this is more commonly a problem when forcing is lacking, which won't really be the case here.

Most SE events indeed feature low LCLs because the you are closer to the Gulf and the environments climatologically are more moist than in the Plains. Low LCLs also mean that storms that mature are more likely to produce tornadoes.
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thanks. Yeah I did post a dozen pages back or so about plains and SE differences in regards to busting
 
jiharris0220 said:
I want to people to keep in mind that what Nixon is saying isn’t one of those big red flag failure modes that slip under the nose and cause a massive Forecasted Convective Amplification Deficiency.

He’s simply highlighting minor monkey wrenches that could prevent Saturday from being a worse case scenario. In which, even the floor would still be devastating.

A day 3 moderate is in every way warranted for this event. It’s simply not possible for a SVR weather threat to not have failure modes, even April 27, 2011 had several.

It’s really just a matter of waiting and watching what the atmosphere does up until that point.
Click to expand...
What were the failure modes for April 27th?
 
jiharris0220 said:
I want to people to keep in mind that what Nixon is saying isn’t one of those big red flag failure modes that slip under the nose and cause a massive Forecasted Convective Amplification Deficiency.

He’s simply highlighting minor monkey wrenches that could prevent Saturday from being a worse case scenario. In which, even the floor would still be devastating.

A day 3 moderate is in every way warranted for this event. It’s simply not possible for a SVR weather threat to not have failure modes, even April 27, 2011 had several.

It’s really just a matter of waiting and watching what the atmosphere does up until that point.
Click to expand...
yup, day before, people had 0 clue if a high would be even issued come d1, then crap hit the fan and was upgraded even further to that 45 near mid day I say?
 
Cyclonic Paracosm said:
yup, day before, people had 0 clue if a high would be even issued come d1, then crap hit the fan and was upgraded even further to that 45 near mid day I say?
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I seem to remember several respected mets talking about the synoptic parameters being higher than they had ever seen leading into April 27th. Would love to hear what the potential failure modes were.
 
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andyhb said:
I'll touch on it. I think there's a little too much "applying Plains logic to the SE" going on here. Low LCLs are commonly concurrent with weak low level lapse rates. Temps need to warm at the surface to steepen low level lapse rates. By definition, if the dewpoint is not rising, this will increase T/Td spreads and lead to LCLs being higher. Should there be some degree of clearing on Saturday, there will be some heating.

Weak low level lapse rates are generally hostile to developing updrafts. With that said, this is more commonly a problem when forcing is lacking, which won't really be the case here.

Most SE events indeed feature low LCLs because the you are closer to the Gulf and the environments climatologically are more moist than in the Plains. Low LCLs also mean that storms that mature are more likely to produce tornadoes.
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I also like to add here that Nixon is indeed correct with the notion that low LCLs can be a detriment if EML and LLJ is to strong. The thing however is that strong LLJs actually helps in mixing out the EML, especially in this case where the LLJ is close to the gulf which means it has a far easier time advecting moist air into the EML.

So I doubt updrafts in the OWS will be thin and weak like in many Dixie Alley setups, unless the forcing is weaker than expected or somehow residual mid level dry air eats away at the convection.
 
TornadoFan said:
Meaning?
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There are two main types of divergence you want to see a loft, which promote broad scale vertical motion.

Divergence is essentially having a wind gradient from slow to fast (think of it as cars exiting a line of traffic into a much clearer road ahead) - air has to fill this gap so vertical motion / rising air is induced.

Diffluence is commonly referred to as divergence but they are slightly different - diffluence is the spreading apart of wind barbs which has the same effect (air needs to fill the gap etc)

In this case I don’t think there is true divergence, which is mainly limited to entrance regions of jet streaks. This looks more like the model resolving some of the convection and enhancing flow slightly as opposed to it being present on the synoptic scale. To be honest in my opinion it’s being used as a bit of a buzzword here because the effect of any “speed divergence” will be negligible compared to the actual forcing via difflunce and height falls from the approaching trough, which will promote likely discrete convection. Hope that made some sense.

Tldr: speed divergence is an important part of diagnosing rising motion but in this case it’s not particularly relevant and the original poster may be slightly overstating the importance in this case (apologies if im coming off a bit harsh)
 
People want certainty. But, as most here are well aware, we just generally don't get a lot of that when trying to forecast gradations of a potential outbreak. I like to think in terms of floors and ceilings when it comes to severe events.

With that said, there's also a balancing act in properly communicating risks BEFORE a higher degree of certainty becomes (hopefully) available on the day of. The upgrade to high on 4/27 is a good example of increasing the forecasted ceiling once some of the potential failure modes were better resolved.

I'm all for this event being underwhelming, however, the chances of that have decreased over the last 24-36 hours. Nonetheless, there's still a lot of new data to take in during the NEXT 24-36 hours which should help our friends at the SPC and NWS have more certainty in their forecast.
 
Evan said:
People want certainty. But, as most here are well aware, we just generally don't get a lot of that when trying to forecast gradations of a potential outbreak. I like to think in terms of floors and ceilings when it comes to severe events.

With that said, there's also a balancing act in properly communicating risks BEFORE a higher degree of certainty becomes (hopefully) available on the day of. The upgrade to high on 4/27 is a good example of increasing the forecasted ceiling once some of the potential failure modes were better resolved.

I'm all for this event being underwhelming, however, the chances of that have decreased over the last 24-36 hours. Nonetheless, there's still a lot of new data to take in during the NEXT 24-36 hours which should help our friends at the SPC and NWS have more certainty in their forecast.
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yup
 
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