Awesome Jim Reed Tornado Footage from ABC News

No need to do any further analysis ... this non-supercell tornado formed when the storm was barely a blip on radar. When the warning box popped up, the storm was barely +35dbz. We were watching the radar pretty hard here in Denver (at least I was) ... saw the warning, did my best whiskey tango foxtrot face and started calling people.
 
To clarify, Jon says he never said landspouts can reach F4 intensity... typically the strongest might get to F2 intensity (Denver metro area has on occasion recorded some low-end F3 damage from them). Maybe someone got confused with Jon's comments about the Jarrell TX tornado (May '97) that appeared to start as a landspout, then morphed into a violent supercell tornado. That was an unusual case with some very different things going on in the environment, not well understood, and certainly not a pure "landspout" event.

Odd, as I thought I recalled that fact - primarily because I found it somewhat shocking. This conversation happened some years ago when I was discussing land spout tornadoes on a Wx-Chase thread. I was pretty sure he responded that way mentioning one case. I keep all my archives..I may be able to find the post. I'll check.
 
Here's a theoretical paper suggesting the ratio for supercell vs. non-supercell F4/F5 tornado correlations:

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"distribution would imply that about 1 out of every 70 supercell tornadoes is violent (F4 or F5), and about 1 out of every 7000 reported non-supercell tornadoes in the United States is violent."
http://www.nssl.noaa.gov/users/brooks/public_html/toulclim.html

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I could swear that someone here at stormtrack mentioned an F4 non-supercell tornado as well. Maybe it was in the education section.
 
Haven't found the reference or email yet, so I may be mistaken. However I did find one from Roger Hill to Wx-chase on landspout strength:

"Landspouts definitely count! I have seen landspouts nearly a quarter mile wide, and causing F2-F3 damage. Just remember in simple terms a landspout forms from the ground up, where a supercell tornado of course forms from the cloud down. Landspouts often form under a wind shift boundary where there is little shear aloft, but decent CAPE and moisture. Along that boundary you get areas of rotating winds that get pulled up into the base of a developing storm. The column of air is stretched and tighted, thus causing it to spin faster. Soon a debris cloud forms on the ground, then a small funnel forms at cloud base and hopefully soon the two will meet :) They often last for more than 15 minutes. And this usually before any rain or even lightning occurs. "

Could have sworn I once had a reference to an F4 landspout.
 
I have found more support for F3 Landspouts:
"From: "Jonathan Triggs" <jtriggs@USWCL.ARS.AG.GOV>
To: <WX-CHASE@listserv.uiuc.edu>
Sent: Friday, July 13, 2001 12:25 PM
Subject: Re: [WX-CHASE] Landspout Winds


> The discussion on landspouts v. tornadoes reminded me of an article
> written by a man that worked closely with Ted Fujita...
>
> Wakimoto, R.M., and J.W. Wilson, 1989: Non-supercell tornadoes. Monthly
> Weather Review, 117, 1113-1140.
>
> The article discussed how small areas of pre-existing circulations can
> be stretched and picked up by convective updrafts to form "non-supercell
> tornadoes." A big example of these conditions is the Denver and Front
> Range areas where there is a nearly persistent convergence boundary.
> When a tight area of positive vorticity becomes collocated with an
> updraft (e.g. cumulus cloud), the results can be explosive...
>
> The article also points out that landspouts can cause damage up to the
> F3 level. Also to note...they referred to the term "landspout" as the
> common expression, but they defined them as tornadoes not associated
> with a supercell.
>
> Jonathan Triggs"

http://ams.allenpress.com/perlserv/...175/1520-0493(1989)117<1113:NST>2.0.CO;2&ct=1

I checked the article and it says capabilities up to F2, but mentions two tornadoes they found matching the landspout definition and one was F3.
 
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