Hurricane-Tornado Threats

[Jeff Snyder]

Originally posted by afischer
Yes, but one can definitely get augmented SRH from a faster storm motion. A typically clockwise hodograph in a tornado set-up in Kansas would have much higher SRH given an incoming 70kt 500mb windmax than with a 40kt 500mb windmax, all else being equal... due to the \"S-R\" part, as u mentioned. And in this light, moderate mid-level flow in a NE hurricane quadrant definitely doesn't \"hurt\" either.

Actually, no, not always. Slower storm motions can increase SRH depending upon the hodograph, particularly for a "classic" clockwise looping hodograph. Note that there is usually an increase in rotation when a supercell slows down and turns to the right (of mean storm motion).

Say this is the SRH with the "mean" storm motion.

This represents the SRH experienced by a storm with a slower storm motion. Note that the SRH is higher.

And this represents that SRH for a storm with a much faster storm motion. Note that the negative SRH nearly equals the positive SRH, so there is very little net SRH.

 

[afischer]

For the record, I clearly didn't say increased storm speed means increased SRH. And I'm not sure what my "increasing midlevel flow 30 knots potentially augments SRH magnitude" example... has to do with a supercell turning right and slowing down... I'll stop now since we are well off-topic. 8)

 

[Jeff Snyder]

Originally posted by afischer
For the record, I clearly didn't say increased storm speed means increased SRH. And I'm not sure what my \"increasing midlevel flow 30 knots potentially augments SRH magnitude\" example... has to do with a supercell turning right and slowing down... that certainly won't help your SRH any! I'll stop now since we are well off-topic. 8)

Since SRH is most often computed from 0-3km or 0-1km, increase mid-level flow will likely to little other than increase storm motion. As I have shown, increased storm motion often DECREASES SRH. If weaker mid-level flow yields slower storm motion, and slower storm motion often increases SRH, then one can indirectly conclude that (given all other favorable conditions and mid-level flow still strong enough to yield adequate deeplayer shear) weaker mid-level flow can help yield higher SRH. You imply (or state) stronger mid-level flow increases SRH, which I argue is exactly the opposite of what really happens (for many supercells). As Glen noted above, computing storm motion (or observing it for that matter) is hardly an exact science, so even forecast SRH has inherent errors associated with errors in storm motion forecasts.

EDIT: I talk of clockwise-looping hodographs and cyclonically-rotating supercells (which is often what we chasers jump for).

 

[afischer]

Thanks for the hodographs... I definitely didn't consider negative SRH in my blanket statement about storm speed's affect on SRH.