Storm modes in unidirectional flow/shear environment

Verhaegen Yoni

Enthusiast
Jun 22, 2019
1
0
1
Belgium
Hi all,

I'm new on the forum but have been passionate with regards to weather and storms for years. Lately, I have been trying to broaden my knowledge on storm development and organization.

Now, I know that DLS (0-6 km shear vector) is used to discriminate between single cells (roughly < 20 kt), multicells (roughly 20-40 kt) and supercells (roughly > 40 kt), but I am wondering what the actual role of unidirectional flow vs. unidirectional shear and directional changes is in these storm modes...

Can a supercell be formed in a unidirectional flow (e.g. SW-lies throughout the whole lowest 6 km, so only speed shear) regime when DLS exceeds 40 kt?

When 20 kt < DLS < 40 kt but unidirectional flow, is it correct that you would most likely see organization into line segments? Does it make a difference to storm modes when most of the shear is comprised in the lower/mid levels or when it is more or less uniformly distributed? Is unidirectional flow (hodograph parallel to its radials) a subtype of unidirectional shear (straight hodograph, not parallel to radials) and hence would you expect similar behavior under a unidirectional shear regime?

I hope I will get some clearance on this one. Thanks in advance!
 

Jeff Duda

Resident meteorological expert
Staff member
Oct 7, 2008
2,986
1,497
21
Westminster, CO
www.meteor.iastate.edu
If you're not familiar with hodographs, now is the time to become so. Any two hodographs that have the same relative shape (e.g., a line) are going to show the same storm behavior regardless of where on the hodograph the wind profile is.

And yes, there is some impact on storm behavior of the vertical distribution of a given amount of wind shear.
 
Nov 18, 2006
1,231
295
11
Chicago, IL
When 20 kt < DLS < 40 kt but unidirectional flow, is it correct that you would most likely see organization into line segments?
A: Yes, more often than not. Discrete modes early on can sometimes get the job done, especially on mesoscale days with boundaries in play.

Does it make a difference to storm modes when most of the shear is comprised in the lower/mid levels or when it is more or less uniformly distributed?
A: Sometimes. You can see more QLCS type events, or embedded supercells within a line. Especially when you've got more speed shear.

Is unidirectional flow (hodograph parallel to its radials) a subtype of unidirectional shear (straight hodograph, not parallel to radials) and hence would you expect similar behavior under a unidirectional shear regime?
A: This one I'm not 100% sure on so I don't want to give too much an answer. I want to say it is not, especially if you're thinking of terms in streamwise vorticity being ingested into your supercell. I believe in those cases you cant parallel vectors but that relates more to your storm direction. I'll let someone else correct me if I'm wrong.
 
Last edited by a moderator: