Landspout in Denver

[Tony Laubach]

Brief/Weak Landspout Tornado in Denver

A different type of chasing today as a weak landspout tornado spun up in the metro area around 345pm. I was working in the 7News studios when our weather intern, Ava spotted the tornado on one of our tower cams. Chief Meteorologist Mike Nelson did a break-in with live images as I phoned NWS with the report. It was pretty exciting as this is the first time I've been working during a tornado event! Good excuse for a steak dinner tonight! Wahoo!

More details and a few more shots on my blog...

 

[Larry J. Kosch]

I wonder why this is called a land spout and not a "dust devil"?? Any reasons or rhymes as to why one term is used and the other is not?? Here in Nebraska its commonly called "dust devils" even though they dont really raise too much dust. LJK

 

[Michael O'Keeffe]

Well it looks to me like there are some tcu above the vortex which most likely makes it a landspout, mainly because in most cases dust devils develop in clear blue skys.

 

[Jeff Snyder]

I wonder why this is called a land spout and not a "dust devil"?? Any reasons or rhymes as to why one term is used and the other is not?? Here in Nebraska its commonly called "dust devils" even though they dont really raise too much dust. LJK

It's sometimes difficult to argue whether a particular land spout should be considered a "tornado", but it's usually easy to say that a dust devil is not a tornado. Dust devils are driven by intense upward motion (usually associated with superadiabatic lapse rates) above a hot surface, and are often located near vertices of boundary-layer convective cells. On the other hand, land-spouts, which can be associated with several different processes, are often associated with a misocyclone (different from a mesocyclone). Sometimes such circulations are associated by flow around and downstream of topograph/orographic features, and other times they are associated with perturbations along a surface boundary (such as a dryline). At any rate, similar to tornadoes, land spouts associated with misocyclones are often the result of strong vertical acceleration aloft that acts to stretch vertical vorticity, and they are often produced when moist convective updrafts move over these misocyclones.

To summarize: it seems that land-spouts associated with misocyclones are still largely driven by the stretching of vertical vorticity that occurs in the updraft of a convective cloud. On the other hand, you can think of dust devils as being driven by intense heating at the surface and convergence at the vertices of boundary layer convective cells. In this manner, dust devils may be thought of as being driven from beneath, while most land spouts can be thought of as being driven by above. Of course, this is very general, so caveat emptor (for example, land spouts too seem to be associated with very steep low-level lapse rates, a condition which may require strong heating at the surface).

I often think of land spouts as non-supercell tornadoes, since they can be directly caused by updrafts associated with deep moist convection (and they can extend to cloud base). The same can't be said for dust devils.

 

[Tony Laubach]

A couple things which helped guide us to our reasoning... first of all, a boundary was moving across the area at the same time which likely enhanced the vorticity at the surface. This boundary was evident on radar imagery before, during, and after the event. Second, there were developing cu in the area including a weak rain shower which developed in the area around the same time.

The NWS office tried to argue it to be a gustnado, to which I would safely say was not the case. With that said, my report was pretty quickly dismissed, which under the circumstances was just fine as there were no other spin-ups after this.

 

[joel ewing]

After living in southern Az. for over 4 decades...my first inclination after looking at the photo was dust-devil. Those clouds over this spinup do not look deep enough to be stretching any vortex. Alas, I know that the photos probably do not do this scenario any justice...and Tony, I know you "know your stuff" and aren't prone to "stretching the vorticity truth!"
Congrats on poppin' yer cherry on air. Now...go get 'ya a nice thick steak!
Joel in Tucson

 

[Shane Adams]

It looks like a dustdevil, but those (along with gustnadoes) move fairly rapidly. I don't know how far apart those pictures were taken, but it doesn't appear to be moving much at all....unless it's moving at the camera I guess.

My question is how long did it last?

 

[Tarmo Tanilsoo]

After living in southern Az. for over 4 decades...my first inclination after looking at the photo was dust-devil. Those clouds over this spinup do not look deep enough to be stretching any vortex. Alas, I know that the photos probably do not do this scenario any justice...and Tony, I know you "know your stuff" and aren't prone to "stretching the vorticity truth!"
Congrats on poppin' yer cherry on air. Now...go get 'ya a nice thick steak!
Joel in Tucson

I thought too that it was a dust-devil - DD's happen every spring in my neighborhood...

P.S. Congrats, Tony!

 

[Tony Laubach]

My question is how long did it last?

We had it on camera for about 5 minutes; it remained nearly stationary the entire time.

 

[Tarmo Tanilsoo]

We had it on camera for about 5 minutes; it remained nearly stationary the entire time.

I will then agree with the landspout thought. None of dust devils I've seen have lasted over 10-15 seconds and been stationary.

 

[Tony Laubach]

Once our intern saw it on camera, we had enough time to look it over, then Mike (the chief met) ran upstairs to fiddle with the camera, get the zoom shot, then come back down and get on air as it fizzled. It was definitely in the five minute area.

We had discussed the possibility of it being a dust devil, but think conditions at the time supported a landspout. Add to that the duration of the event, its very little movement, developing storms along a boundary, and I think we made the right call.

 

[Tarmo Tanilsoo]

I am wondering, if anybody managed to take any videos of that landspout?

 

[Tony Laubach]

I am wondering, if anybody managed to take any videos of that landspout?

I believe we had the event on timelapse which won't show the realtime since frames were being captured every 30 seconds. I'll check with the station today and see if I can get something posted.