Let's have a look at some old skew-ts.

[Teru Teru Bozu]

Because the weather is a tad boring uneventful right now and I was itching to do a little thought experiment.

I want to give a shout-out to the University of Wyoming for this excellent page:

 

http://weather.uwyo.edu/upperair/sounding.html

 

It's a great resource for severe weather enthusiasts who like to review past events, and it's interesting to compare and contrast them by way of the upper air sounding plots. I looked up the skew-t plots for varous historic severe weather events, and each one caught my eye in some way or another, as I'll post below. Feel free to post data or thoughts on a severe weather event that you find interesting, too. And if you need info on how to read skew-ts or interpret severe weather indices, this page is a good start: http://www.theweatherprediction.com/thermo/parameters/

 

History in the Making - 3 April 1974

 

The Sounding:

 

This profile has just about anything you'd look for leading up to a major severe weather outbreak: high instability (as the LI, TT, and CAPE show), lots of speed and directional shear, and a strong-but-not-too-strong cap. The wind profiles suggest that the environment is prime for supercell development. The vigorous upper-level southwesterly jet that overlaid the whole event is visible on this chart (up to 95 kt at 300 mb).

 

The Result:

 

The most violent tornado outbreak in U.S. history. Most of the tornadoes in the Super Outbreak were spawned in families by numerous long-lived supercells, as can be seen in the satellite loop.

 

http://en.wikipedia.org/wiki/Super_Outbreak

[Teru Teru Bozu]

Black Friday - 31 July 1987

 

The Sounding:

 

 

 

This is an interesting one to look at. It isn't really a "classic" profile for a multiple supercell outbreak or anything; there is fairly decent directional shear at the low levels, but not all that much above (and, in fact, the sounding indicates a southEASTERLY jet above 300 mb!). There is good speed shear, though, and high instability with capping. So, you might expect some intense linear storms more than lots of discrete cells. Given that this sounding was taken in central Alberta, as opposed to the southern U.S. Plains, I am impressed by the amount of low-level moisture that was present (dewpoints in the low-mid 60s F).

 

The Result:

 

 

On the afternoon of 31 July, a supercell formed out ahead of a line of severe thunderstorms headed in the direction of Edmonton, AB (did the supercell form as a result of outflow from the squall line? I'd love to see a radar loop of this event). It quickly turned to the north (perhaps under the influence of the upper level south/southeasterly jet) and spawned a massive, multi-vortex tornado that did F4 damage on the east side of Edmonton. It is the northernmost known violent tornado in North America. 

 

http://en.wikipedia.org/wiki/Edmonton_Tornado

 

[Teru Teru Bozu]

Fuel to the Fire - 29 June 2012

 

The Sounding:

 

The first thing that jumps out at me here is the CAPE. Look at all that CAPE! This sounding was taken in the midst of a major heat wave in the southern and eastern U.S., with surface temps in the low 100s in parts of the Mid-Atlantic and Southeast. As you might expect, there's a lot of low-level moisture to go around, too. But not really a strong cap to speak of, OTOH. Shear is not all that much to write home about, either, particularly the directional shear. Speed shear is okay. This profile doesn't really support supercell development, but whatever storms do happen to form will have plenty of fuel from the strong surface heating and moisture available.

 

The Result:

 

 

 

Derecho! What started out as a modest cluster of thunderstorms in central Iowa gradually developed into an intense squall line of storms that caused widespread wind damage from the Midwest all the way to the Mid-Atlantic coast. The extemely warm, moist air mass that the line encountered helped it to grow and strengthen, and many locations along the path saw wind gusts of 70 mph or more (peak gust was 91 mph at Ft. Wayne, IN). While not the strongest or longest-lived derecho ever seen in North America, it grabbed headlines because of the major population centers it affected.

 

http://en.wikipedia.org/wiki/June_2012_North_American_derecho

 

[OKpowdah]

May 24, 2011 Oklahoma

 

The sounding 

 

 

The result

 

http://www.srh.noaa.gov/oun/?n=events-20110524

[Ed Lizard]

May 24, 2011 Oklahoma

 

The sounding 

 

2011052418.72357.skewt.gif

 

The result

 

http://www.srh.noaa.gov/oun/?n=events-20110524

 

 

That is a pretty stout cap, if I saw that on a special 18Z LCH sounding, I'd surrender all hope.  (Obviously SPC requested that sounding because model guidance suggested otherwise)  Which reminds me, HGX or EWX should have balloons.  Texas is ringed with sounding sites, but has a vast hole in the middle.  I have to hope HGX mentions strength of capping from ACARS in a forecast discussion update or rely on short term models.  HRRR seems too optimistic in breaking the cap locally.

[Teru Teru Bozu]

May 24, 2011 Oklahoma

 

The sounding 

 

http://www.americanwx.com/bb/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=95563'>2011052418.72357.skewt.gif

 

The result

 

http://www.srh.noaa.gov/oun/?n=events-20110524'>http://www.srh.noaa.gov/oun/?n=events-20110524

That's quite a classic S. Plains tornado sounding (and only two days after the Joplin tornado...what a week). Look at that cap...

I didn't know that the El Reno-Guthrie tornado was rated (EF5) based at least in part on DOW wind speed estimates. Is this the first time this had been done? Obviously the tornado did a tremendous amount of damage as well.

[Ed Lizard]

The UWyo didn't want to develop soundings for a specific date/time station where I was looking for a uber-low tropopause in 1979.

 

But I figured I could look at nearby stations on significant weather days locally.

 

 

[thewxmann]

The one and only...

 

[Teru Teru Bozu]

The one and only...

 

That's a very impressive dry slot aloft. Plus the shear is just about as strong as you'll ever see...easy to understand what happened next.

 

Here's another storm I find interesting...

 

Night of the Twisters - 3 June 1980

 

The Sounding:

 

 

Tons of instability here, and strong directional shear, but not too much speed shear. I'm not sure if helicity and mean storm motion were used as severe weather indices back in 1980, but note the relatively light winds up to about 400 mb.

 

The Result:

 

 

 

The Grand Island tornado outbreak of 1980 was among the most complex ever surveyed. It was characterized by a very slow-moving (likely thanks to those lighter winds aloft) but intense supercell that spawned seven tornadoes as well as several downbursts in or near the city over a period of about 3 hours. Three of the tornadoes were anti-cyclonic (remarkable considering that perhaps 1-2% of ALL tornadoes are thought to rotate anticyclonically), and even those that weren't followed erratic or looping paths. If you're like me, you probably http://www.gitwisters.com/bookmovie/twistersauthor.php'>read this book a whole lotta times when you were little (or older). The book gives you a sense of both the duration and the complexity of the outbreak, which truly must have been a nightmare for anyone who went through it. "Even Dr. Fujita, the great tornado wizard, was baffled."

 

http://en.wikipedia.org/wiki/1980_Grand_Island_tornado_outbreak

[AgeeWx]

One of my favorite soundings to look at only because I sat on my roof and watched this thing roar across Northern Illinois.

 

http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=GIF%3ASKEWT&YEAR=2008&MONTH=08&FROM=0412&TO=0500&STNM=74455

[AgeeWx]

http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=GIF%3ASKEWT&YEAR=1990&MONTH=08&FROM=2812&TO=2900&STNM=72532

 

And then of course there's the sounding from Central Illinois the day of the Plainfield tornado. Station is about 100 miles south of where tornado occurred and was from 3+ hours after TOG and it was still incredibly unstable. WRF reanalysis suggests environment near Plainfield at the time of the tornado was near 9000 J/kg of CAPE with bulk shear of about 30kts.

[Hoosier]

http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=GIF%3ASKEWT&YEAR=1990&MONTH=08&FROM=2812&TO=2900&STNM=72532

And then of course there's the sounding from Central Illinois the day of the Plainfield tornado. Station is about 100 miles south of where tornado occurred and was from 3+ hours after TOG and it was still incredibly unstable. WRF reanalysis suggests environment near Plainfield at the time of the tornado was near 9000 J/kg of CAPE with bulk shear of about 30kts.

The environment on the day of the Plainfield tornado was jacked...temps in the 90s and dewpoints well into the 70s in the immediate area of the tornado with steep lapse rates so it's no wonder why instability was so high. But the maps that day didn't necessarily scream big tornadic trouble. It may be one of the more fluky F5s and also kinda unique since it received that rating based on damage to crops.

[Teru Teru Bozu]

The environment on the day of the Plainfield tornado was jacked...temps in the 90s and dewpoints well into the 70s in the immediate area of the tornado with steep lapse rates so it's no wonder why instability was so high. But the maps that day didn't necessarily scream big tornadic trouble. It may be one of the more fluky F5s and also kinda unique since it received that rating based on damage to crops.

 

I hadn't heard about the F5 rating being based on crop damage, that's interesting. I've seen video of the damage from the Plainfield storm and there was certainly a lot of devastation, with many cases of borderline F4/F5 damage to homes. I do recall hearing that there was a LOT of controversy because no tornado warning was issued until after the tornado had actually hit. This was in the pre-Doppler era, and apparently spotter reports were not properly relayed to the local NWS office until it was too late.

[nwburbschaser]

Speaking of the Plainfield tornado, can anyone post a sounding that shows tornado potential in a northwest flow situation??

[Teru Teru Bozu]

Speaking of the Plainfield tornado, can anyone post a sounding that shows tornado potential in a northwest flow situation??

 

Well, here's one from 1979 that shows predominantly NW flow in the upper levels. To the west of this station, there was a localized but powerful outbreak of tornadoes (including two F4s) in and around Woodstock, Ontario.

 

 

http://en.wikipedia.org/wiki/1979_Woodstock,_Ontario_tornado

 

Seems like a type of pattern more likely to produce tornadoes/severe weather in the summer, for whatever reason. There have been several major derecho/MCS events that have also developed in NW flow, and those are generally summertime systems.

[andyhb]

Skew-T/Hodograph from Pittsburgh, PA on the evening of 5/31/85.

 

From BMX on the evening of April 8th, 1998.

[Teru Teru Bozu]

Skew-T/Hodograph from Pittsburgh, PA on the evening of 5/31/85.

 

This was quite an impressive tornado outbreak, especially considering the area. The long track tornado in Central PA (#29) was over 2 miles wide at times and mowed down almost 100,000 trees in a state forest.

 

[Hoosier]

I hadn't heard about the F5 rating being based on crop damage, that's interesting. I've seen video of the damage from the Plainfield storm and there was certainly a lot of devastation, with many cases of borderline F4/F5 damage to homes. I do recall hearing that there was a LOT of controversy because no tornado warning was issued until after the tornado had actually hit. This was in the pre-Doppler era, and apparently spotter reports were not properly relayed to the local NWS office until it was too late.

Yeah, the peak damage to structures was more in the F3 to F4 range, which is obviously bad enough. If this tornado were to occur today, it probably couldn't be rated EF5 since there isn't an EF5 damage indicator for crops. I believe that Fujita remarked that this was the strongest tornado he had personally surveyed.

[Teru Teru Bozu]

Yeah, the peak damage to structures was more in the F3 to F4 range, which is obviously bad enough. If this tornado were to occur today, it probably couldn't be rated EF5 since there isn't an EF5 damage indicator for crops. I believe that Fujita remarked that this was the strongest tornado he had personally surveyed.

I'd imagine you'd need a very experienced and trained eye to rate a tornado based on damage to plants (much as some tornadoes were rated based on damage to structures that an engineer would have to examine personally). I think tree damage might be used as damage indicators at some levels of the Enhanced Fujita Scale, though - or, at least, extensive tree debarking is generally acknowledged to indicate winds of near violent intensity.

I recall reading about a violent tornado that hit the Teton Wilderness of Wyoming back in the '80s. Fujita rated it at F4 based primarily on tree damage, with the caveat that the actual wind speed of the tornado may have been even HIGHER than indicated by the damage due to the high altitude (10,000+ feet). It is the highest elevation violent tornado ever recorded.

[Jim Marusak]

This was quite an impressive tornado outbreak, especially considering the area. The long track tornado in Central PA (#29) was over 2 miles wide at times and mowed down almost 100,000 trees in a state forest.

 

 

and a related sounding for this outbreak was the one from Flint  MI (72637)

 

http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=GIF%3ASKEWT&YEAR=1985&MONTH=05&FROM=3112&TO=3112&STNM=72637

 

reason why that's important, that would be the part of the air mass that formed the Barrie f-4 Tornado in that outbreak.

[Jim Marusak]

http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=GIF%3ASKEWT&YEAR=2009&MONTH=04&FROM=1012&TO=1012&STNM=72340

 

i know this wasn't the biggest outbreak in the world back in 2009 on april 10th. but this one was a significant to me because it was the first tornado coverage I did on the air with live updates for an affiliate, WGNS in Murfreesboro. seeing multiple funnels in Rutherford county, TN, yea, it was a smaller radio station, but when you're hearing storm damage reports coming in live for the first time, hearing the nurses and docs being called in for the triage units live on the air, you remember that moment for a long time.

[TropicalAnalystwx13]

Sounding from Newport, NC on the afternoon of the worst tornado outbreak recorded in our state's history:

 

[Teru Teru Bozu]

Sounding from Newport, NC on the afternoon of the worst tornado outbreak recorded in our state's history:

 

 

What's crazy about April 16 was that it wasn't even close to being the worst outbreak of the year (sadly...), but it was incredibly intense for our area. That seemed to happen a lot that year, strong tornado events in all corners of the country, some of which don't usually see them (see also: the Springfield, MA tornado of June 2011).

 

That shear was just ridiculous, though. I like this radar still from the middle of the outbreak, with four tornadic supercells going simultaneously: