F5/EF5 Tornadoes in non-typical conditions

[Peter Griffin]

So from what I've read the recent Cookeville EF4 what a bit of an over performer. You wouldn't typically expect a tornado that powerful in those conditions.

Just got me wondering if there are any F5/EF5 tornadoes 'over-achieved' and were more powerful than expected given the conditions. Cape to low? Not enough wind shear? ETC

From what I've read the Jarrell tornado kinda falls in that category. There was ample instability but outside of that it wasn't really a typical set-up we are use to seeing.

If anybody knows of any storms like this it would be greatly appreciated if you share your knowledge. Thanks!

 

[akt1985]

I don’t know if this counts, but I hear the Plainfield, Illinois F5 from 1990 occurred during a Severe Thunderstorm Watch and not a Tornado Watch.

 

[gangstonc]

I think Jarrell was somewhat atypical. Not a ton of shear, but tremendous instability if i remember correctly.

 

[Peter Griffin]

I don’t know if this counts, but I hear the Plainfield, Illinois F5 from 1990 occurred during a Severe Thunderstorm Watch and not a Tornado Watch.

I have read about this tornado but for but haven't delved a whole lot into the setup. Will have to look in to that. Everything I read says this tornado was EXTREMELY violent. Also seems like I remember it was a pretty unusual event for that area given the time of the year.

 

[Peter Griffin]

I think Jarrell was somewhat atypical. Not a ton of shear, but tremendous instability if i remember correctly.

Yeah quite an event. A gravity wave and a dry line interacted and storms absolutely exploded along the line. Storms had a 'zipper' effect building from NE to SW. Crazy stuff.

 

[Peter Griffin]

https://www.wunderground.com/cat6/twenty-years-look-back-jarrell-tornado-catastrophe great article about Jarrell. Also it lists a couple of other F5 tornados that formed in high instability, low wind shear environment. Plainfield in 1990 was one of them.

 

[Shakespeare2016]

I know of a couple tornadoes rated high-end F4 on the original F-scale that occurred in atypical conditions. The Harper, Kansas tornado on May 12, 2004 and the Barnes County, North Dakota on July 18, 2004. They both occured in like 2-5% areas for tornadoes. The Harper, Kansas tornado easily could have been rated F5 and the Barnes County, North Dakota possibly could of as well.

 

[Equus]

The extremely high end Chapman KS EF4 on 5/25/16 comes to mind; occurred on what was a Marginal risk for Kansas until 1630z, and only a 2% tor risk until 2000z... strong capping and little forcing for ascent precluded higher probabilities as most models didn't want to initiate convection at all if I recall, and the supercell that dropped that long track violent tornado was essentially the only radar echo in Kansas for most of its lifespan aside from brief showers that died. I remember being at the county fair watching the radar absolutely incredulously as that tornado churned eastward.

Plainfield was weiiird. Nothing about that tornado made sense. A southeast moving F5 in an HP supercell in the Chicago suburbs in August. I really want to read some research into that one. And yeah Jarrell is absolutely the poster boy for extreme CAPE/low shear events where boundaries make all the difference.

Cookeville still seems like a baffling enigma though. Obviously the massive >600 m2s2 0-1km srh in that little pocket would support violent tornadoes but nothing else about that environment made me think a cell would be able to thrive and take advantage of said shear.

Oh! Another extremely weird one, the 4/4/81 West Bend, WI tornado; a middle of the night anticyclonic F4 on the ground for only two miles and 50 yards wide, killing three and leveling two story houses, out of a low topped weakening bow echo with no indication of rotation. That one has some fascinating research paperwork.

 

[Peter Griffin]

The extremely high end Chapman KS EF4 on 5/25/16 comes to mind; occurred on what was a Marginal risk for Kansas until 1630z, and only a 2% tor risk until 2000z... strong capping and little forcing for ascent precluded higher probabilities as most models didn't want to initiate convection at all if I recall, and the supercell that dropped that long track violent tornado was essentially the only radar echo in Kansas for most of its lifespan aside from brief showers that died. I remember being at the county fair watching the radar absolutely incredulously as that tornado churned eastward.

Plainfield was weiiird. Nothing about that tornado made sense. A southeast moving F5 in an HP supercell in the Chicago suburbs in August. I really want to read some research into that one. And yeah Jarrell is absolutely the poster boy for extreme CAPE/low shear events where boundaries make all the difference.

Cookeville still seems like a baffling enigma though. Obviously the massive >600 m2s2 0-1km srh in that little pocket would support violent tornadoes but nothing else about that environment made me think a cell would be able to thrive and take advantage of said shear.

Oh! Another extremely weird one, the 4/4/81 West Bend, WI tornado; a middle of the night anticyclonic F4 on the ground for only two miles and 50 yards wide, killing three and leveling two story houses, out of a low topped weakening bow echo with no indication of rotation. That one has some fascinating research paperwork.

Awesome info thanks for sharing! Definitely gonna see if I can find some info on that West Bend tornado sounds fascinating!

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[Shakespeare2016]

Chapman practically caused EF5 damage as far as I am concerned. Also the Moore, Oklahoma EF5 tornado on May 20, 2013 was only in a 5% area with a regular tornado watch. There was a 10% hatched area that day but it was further south.

 

[Equus]

Here's the MWR article that discusses the West Bend tornado - I can imagine a lotta people were nervous around every squall like for a long time lol

 

[Peter Griffin]

The Jordan, Iowa F5 is another high instability low shear tornado. Most people on the board have probably already read about this one as it is pretty well known. Fascinating storm for a number of reasons. A couple examples are its unusual track and the fact it was accompanied by an unusually strong anti-cyclonic tornado which basically paralleled its path. Also there is evidence to support another smaller satellite tornado which rotated around the main tornado at times.