Which is more important....High Instability or Strong Shear?

[JamesCaruso]

It is the balance that is important and, of course, ideally want optimal levels of both, but anecdotally I think high CAPE days have more potential for a mesoscale accident.

I remember seeing a great chart somewhere that plotted historical events that showed the correlation of CAPE/shear, but I can’t remember where. Perhaps one of the links earlier in this thread were to that chart, but both links are no longer active.

 

[Ethan Schisler]

It is the balance that is important and, of course, ideally want optimal levels of both, but anecdotally I think high CAPE days have more potential for a mesoscale accident.

I remember seeing a great chart somewhere that plotted historical events that showed the correlation of CAPE/shear, but I can’t remember where. Perhaps one of the links earlier in this thread were to that chart, but both links are no longer active.

Is this the image that you are referencing? Its from Jon Davies' website. I corrected my previous post because I found an updated plot that he created this year.

 

[Stan Rose]

I'd take high instability alone over high shear every time. Shear can't create instability, but instability can create shear, in the form of SRH. I remember chasing a storm about 20 years ago in southern Nebraska where the winds were below 20 kts from 500mb down, but CAPE was huge. And it produced a bunch of funnels and golf ball hail. Regardless of tornado potential, the high CAPE storms are almost always more visually impressive than the high shear ones. your mileage may vary.

 

[JamesCaruso]

@Ethan Schisler Yes I think that's the one, thanks!

 

[rsheeler]

The Jarrell TX 1997 event seems to be one of those strange cases of a setup that had huge CAPE instability with relatively low shear as mentioned on this forum before. Of course the stalled front and gravity wave movement definitely played into that. (btw, is the gravity wave the same as an outflow boundary in the nomenclature?). All in all, it seems like there are any number of possible setup scenarios that have led to tornado formation over the years.

 

[Jeff Duda]

(btw, is the gravity wave the same as an outflow boundary in the nomenclature?).

Apologies for going off-topic, but no, outflow boundaries and gravity waves are very much separate entities (although large thunderstorm outflows can generate gravity waves, but the causal relationship only goes in that direction).

 

[rsheeler]

Apologies for going off-topic, but no, outflow boundaries and gravity waves are very much separate entities (although large thunderstorm outflows can generate gravity waves, but the causal relationship only goes in that direction).

thanks for that. I had often wondered about that.

 

[Dean Baron]

Apologies for going off-topic, but no, outflow boundaries and gravity waves are very much separate entities (although large thunderstorm outflows can generate gravity waves, but the causal relationship only goes in that direction).

Sorry to continue going off topic with this but to build off your point gravity waves can also generate additional lift. Some of the stronger tornadoes were the result of a storm firing from a gravity wave in an otherwise capped environment. I believe the Joplin and Parkersburg, IA EF5's are a couple of examples of storms firing from a gravity wave, though I could be wrong about that.