Has there ever been an "F6" tornado?

[bigfoot3000]

http://www.datarecovery.com/tornado.asp
What kids of circumstances would it take for one of these to form?

[Clanad]

No... at least not as far as we know. The strongest tornado recorded here in the U.S. happened in "Tornado Alley" parts of Texas, Kansas and Oklahoma) on May 3, 1999, and was rated as an F-5 with recorded winds from 261-319 mph. Although the Fujita Scale includes F6, winds exceeding 319 mph have not been recorded.

There was a severe tornado back in 1928 in the State of Missouri (just northeast of the conventional Tornado Alley) that may have had winds in excess of 319 mph, but the recording devices of the era weren't accurate enough to frame the winds.

The fact is that damage caused by F5's is so severe that, lacking actual measurement of winds, the move into F6 would not be recognizable when considering only the damage...

Here's view of the F5 in OKC... it, apparently only missed being an F6 by a few mph...

https://www.youtube.com/watch?v=W19qa-AK8Dk

[bigfoot3000]

Cheers clanad!