The tornado season of 2008: climate change to blame? And, tropical update

By: Dr. Jeff Masters , 5:07 PM GMT on May 27, 2008

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Residents of Parkersburg, Iowa continue to assess damage and clean up from the tornado that killed six people on Sunday. The tornado was rated EF-5, the highest possible rating for a tornado. An EF-3 tornado also hit Hugo, Minnesota on Sunday, killing one person. Only five new tornado reports occurred yesterday, and severe weather is expected to remain relatively low for the next two days. A new storm system is expected to bring an enhanced chance of severe weather to the upper Midwest beginning Thursday. The deaths Sunday push this year's tornado death toll to 110. This makes 2008 the 12th deadliest tornado season since 1950, and the deadliest since 1998, when 130 deaths were recorded. Assuming that the Parkersburg, Iowa tornado was an EF-4 or EF-5, there have been nine violent EF-4 or EF-5 tornadoes this year. This is the most since 1999, when 13 such twisters were recorded. The total (preliminary) number of tornadoes so far this year is 1191. I doubt that we will break the all time record of 1817 tornadoes in a year, set in 2004, but 2008 may vault into second place if we can top 1998's 1424 tornadoes. Could this year's tornadoes be a sign of climate change?


Figure 1. Tornadoes deaths in the U.S. by year since 1950. Year 2008 deaths are as of May 26.

Well, let's be clear that human-caused climate change is occurring, and will significantly affect nearly all aspects of weather and climate in the decades to come. However, many of these changes will be so small or gradual that they will not become detectable until many decades hence, since there is a large natural variability in weather. As I noted in my February blog, Are tornadoes getting stronger and more frequent?, there is new research that predicts that we may see an increase in the severe thunderstorms that spawn tornadoes by the end of the century. However, the computer modeling efforts that predict this rise in severe weather are just beginning, and much more research remains to be done before we can believe these preliminary results.

Will we be able to detect changes in tornado frequency if they occur?
We won't be able to detect changes in tornado frequency due to climate change, unless there is a very large change. We need a technology that can detect all tornadoes, all the time in order to be able to evaluate changes in tornado frequency. Doppler radar can only "see" perhaps 50% of all tornadoes, and many of those it detects never touch down. Thus, we rely on human observers to spot tornadoes, or look for buildings that got in the way of a tornado, using the damage pattern to identify a tornado. If there are no humans around to see a tornado, and if a tornado does not encounter any structures, it will go unrecorded. As the population increases and more buildings are erected, tornado reports will increase. This factor alone can account for the observed increase in total tornadoes since 1950 (Figure 2).

Is there evidence that strong and violent tornadoes are increasing?
Strong tornadoes (EF2 and EF3 on the Enhanced Fujita Scale) and violent tornadoes (EF4 and EF5, or F4 and F5 on the pre-2007 Fujita Scale), which make up less than 25% of all tornadoes, cause a large fraction of the tornado deaths. These storms are less likely to go uncounted, since they tend to cause significant damage along a long track. Thus, the climatology of strong and violent tornadoes may offer a clue as to how climate change may be affecting severe weather. Unfortunately, we cannot measure the wind speeds of a tornado directly, except in very rare cases when researchers happen to be present with sophisticated research equipment. Tornadoes are categorized using the Enhanced Fujita (EF) scale, which is based on damage. So, if a strong or violent tornado happens to sweep through empty fields and never destroy any structures, it will not get a rating. Thus, if the number of violent tornadoes has actually remained constant over the years, we should expect to see some increase in these storms over the decades, since more buildings have been erected in the paths of tornadoes.

However, if we look at the statistics of strong and violent U.S. tornadoes since 1950 (Figure 2), there does not appear to be any increase in the number of these storms. In fact, there appears to be a decrease, although the quality of the data base is probably not good enough to say this with confidence. It appears likely that climate change has not caused an increase in the strongest tornadoes in recent decades. I believe we can blame 2008's nasty tornado season on an unusually far south loop that the jet stream has taken this year over the U.S., thanks to natural variability in the weather.


Figure 2. Total, strong and violent tornadoes in the U.S. by year since 1950. The year 2008 (not pictured) has had 128 strong or violent tornadoes as of May 26, according to Wikipedia.

Possible development in the Western Caribbean or Eastern Pacific late this week
A weak low pressure area (Invest 90E) has developed in the Eastern Pacific off the coast of Guatemala, near 10N 90W. This low has the potential to develop into a tropical depression by the end of the week, according to the UKMET model. Other models, such as the GFS, Canadian, and ECMWF, foresee that this area of disturbed weather will not have time to develop before moving northwards over Central America by the end of the week, bringing heavy rains to the region. Once over land, this low might move over the waters of the Western Caribbean and allow a tropical depression to form, as predicted by the GFS model. The NOGAPS model, in contrast, predicts that a tropical depression will form in the Western Caribbean south of Cuba, with no development in the Eastern Pacific. Given the persistence of these computer models over the past week in developing something in the region, I'd put the odds of a tropical depression forming within 7 days at about 40% in the Eastern Pacific, and at 20% in the Western Caribbean. There is a lot of wind shear predicted to prevail near or over the Western Caribbean late this week and early next week, reducing the odds that any such development could hold together long enough to affect the U.S. Regardless, residents of Guatemala, El Salvador, Honduras, Belize, and southern Mexico can expect heavy rains and possible flash flooding late this week from this system.


Figure 3. Area of disturbed weather over the Eastern Pacific that is forecast by some models to develop into a tropical depression. The NHC Graphical Tropical Weather Outlook is a good tool to track this disturbance.

I'll have an update by Wednesday afternoon.

Jeff Masters

New Hartford (snp4u)
Missing House, if found call Dennis and Carla
New Hartford
New Hartford (snp4u)
car pile up
New Hartford
Supercell near Pratt, Kansas (MikeTheiss)
Nice structure on upercell east of Pratt, Kansas. Photo copyright Mike Theiss.
Supercell near Pratt, Kansas

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938. kmanislander
2:45 AM GMT on May 28, 2008
890. Swells22 2:32 AM GMT on May 28, 2008
Hey can I get a little educated here as a tropical storm amateur? How can one tell a ULL from the vapor loop.

Upper level lows occur, as you might expect from the name, in the upper levels of the atmosphere. The water vapour loop is showing moisture in the atmosphere at those levels.

A low spins counterclockwise so a counterclockwise spin on the WV loop is a ULL because it is a low in the upper levels

This may not be a scientific explanation but it is the best I can do as a blogger !

Anyone else have a better explanation ?

It's just one of those things you learn to recognise when you see it
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937. Orcasystems
2:51 AM GMT on May 28, 2008
Thank you :) JP
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935. Orcasystems
2:47 AM GMT on May 28, 2008
JP, another stupid question.. which model is the Canadian Model?
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934. weatherblog
2:47 AM GMT on May 28, 2008
*922

You can find NOGAPS here.
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933. IKE
9:47 PM CDT on May 27, 2008
924. jphurricane2006 9:42 PM CDT on May 27, 2008
lol IKE, congrats to you

hope you didnt just jinx yourself lol


Thanks!!!!
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932. Drakoen
2:46 AM GMT on May 28, 2008

Member Since: October 28, 2006 Posts: 57 Comments: 30355
931. Tazmanian
7:45 PM PDT on May 27, 2008
yes nrtiwlnvragn has you where the olny one on here new what i was talking about thanks
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930. shoreacres
9:43 PM CDT on May 27, 2008
Moonlight ~

re: #916 Lurking and learning
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929. weatherblog
2:41 AM GMT on May 28, 2008
90E is sure improving from this morning... I still don't think TD currently, but maybe by tomorrow if it keeps it's organization up. Also, it would have to move north a little bit, or it will run into Costa Rica/Panama.
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928. TampaSpin
10:42 PM EDT on May 27, 2008
If he has munchies its not because of staying up.......LMAO
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927. Drakoen
2:43 AM GMT on May 28, 2008
Jp, i'm an ex-convict lol.
Member Since: October 28, 2006 Posts: 57 Comments: 30355
926. Drakoen
2:42 AM GMT on May 28, 2008
923. JFV 2:42 AM GMT on May 28, 2008
Drak, you staying up to watch the midnight munchies?


Nope.
Member Since: October 28, 2006 Posts: 57 Comments: 30355
925. Swells22
2:41 AM GMT on May 28, 2008
Yeah, I picked the wrong blog to ask an honest question!
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922. SpaceThrilla1207
2:41 AM GMT on May 28, 2008
Link me to the path of the NOGAPS. Someone said it was very interesting.
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920. TampaSpin
10:40 PM EDT on May 27, 2008
Looks like insanity is starting.....but, this year i know where the sanity lies...if ya know what i mean....lol
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919. nrtiwlnvragn
10:40 PM EDT on May 27, 2008
Taz,

You get that other spaghetti plot link I posted?

868. nrtiwlnvragn
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918. IKE
9:40 PM CDT on May 27, 2008
Not that anyone cares...or should...but, I'm over 8,000 posts on WU without one banning(self-glossing).
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917. Drakoen
2:39 AM GMT on May 28, 2008
Poor 90E is not getting any attention as it slowly becomes better organized.
Member Since: October 28, 2006 Posts: 57 Comments: 30355
916. moonlightcowboy
9:39 PM CDT on May 27, 2008
Hey, Shoreacres! You getting in with us on the tropics? Glad to have you here!
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915. Tazmanian
7:39 PM PDT on May 27, 2008
hi TampaSpin
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914. TampaSpin
10:39 PM EDT on May 27, 2008
Hey Jp....lol
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913. kmanislander
2:38 AM GMT on May 28, 2008
yeah Drak the low with 90E is not too impressive at this time
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911. nash28
2:38 AM GMT on May 28, 2008
Ok, before I go scanners on someone else because I am tired, I am OUT.
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910. TampaSpin
10:37 PM EDT on May 27, 2008
Hi Nash, Taz and Drak
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909. BahaHurican
10:36 PM EDT on May 27, 2008
904.
Cape Verde.
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907. shoreacres
9:37 PM CDT on May 27, 2008
Ah! Of course. Thanks, Nash
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906. nash28
2:36 AM GMT on May 28, 2008
Cape Verde Shoreacres.
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905. TampaSpin
10:35 PM EDT on May 27, 2008
looks like i logged on at a bad time...lol
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904. shoreacres
9:34 PM CDT on May 27, 2008
OK, guys - time out to enlighten a weather doofus. I've been trying to find the meaning of the abbreviation "CV" and haven't. What does it stand for?
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903. Orcasystems
2:31 AM GMT on May 28, 2008
Not bad.. read about 600 posts.. found some good comments... two minus's checked...and BH used one of the three bad words :)
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902. Tazmanian
7:35 PM PDT on May 27, 2008
right the Admins could be watching
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901. Drakoen
2:35 AM GMT on May 28, 2008
898. nash28 2:34 AM GMT on May 28, 2008
Most of us are Drak.

You know that.


Yea thats the sad part.
Member Since: October 28, 2006 Posts: 57 Comments: 30355
900. Drakoen
2:34 AM GMT on May 28, 2008
885. kmanislander 2:30 AM GMT on May 28, 2008
Quikscat this evening places the low at 87W and 9 N approx

Link


The high resolution images shows an elongated area of low pressure but it looks to be closing up a bit from the last pass.
Member Since: October 28, 2006 Posts: 57 Comments: 30355
899. IKE
9:34 PM CDT on May 27, 2008
gosh...this blog....I know I am at the right one.
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898. nash28
2:34 AM GMT on May 28, 2008
Most of us are Drak.

You know that.
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897. HadesGodWyvern (Mod)
2:32 AM GMT on May 28, 2008
896. Drakoen
2:33 AM GMT on May 28, 2008
Jeez you guys can't go one day without drama. Grow up.
Member Since: October 28, 2006 Posts: 57 Comments: 30355
895. weatherblog
2:32 AM GMT on May 28, 2008
Just ignore the second troll of the night.
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894. nash28
2:32 AM GMT on May 28, 2008
If that is the case MLC, an LOL afterwards would go a long way.

Anyone attacking my friends will get response from me.
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893. moonlightcowboy
9:33 PM CDT on May 27, 2008
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892. CaneAddict
2:30 AM GMT on May 28, 2008
Wow in the 2-3 years i have been here in one night i have added 2 folks to my ignore list....and the only 2 on my list.

Night all!
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891. moonlightcowboy
9:31 PM CDT on May 27, 2008
Chill folks, I'm sure that's meant as more of a running, joking chin-wag between those fellas.
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890. Swells22
2:25 AM GMT on May 28, 2008
Hey can I get a little educated here as a tropical storm amateur? How can one tell a ULL from the vapor loop. This is in reference to the statement:

"there is a ULL over Guatemala driving 90E due E"
-Thanks!
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888. weatherboykris
2:30 AM GMT on May 28, 2008
Yeah vortix. Why are you trying to start something? We're just talking weather here, for once with no arguments.
Member Since: December 9, 2006 Posts: 125 Comments: 11346

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.