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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38. Patrap
12:35 PM CDT on May 27, 2008
Naw..that Co2 Fairy comes out every Night and Waves the Ol ,,"Its Okay,Dont worry Wand"..
LOL
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37. moonlightcowboy
12:34 PM CDT on May 27, 2008
...from Dr. Masters:

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.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
36. nash28
1:33 PM EDT on May 27, 2008
Presslord- Certifications and a meteorology degree does not make ANYONE an authority on whether man is causing destructive climate change. The fact is that NO ONE KNOWS!
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35. presslord
1:27 PM EDT on May 27, 2008
yea..Masters couldn't possibly have any credibility on the subject...

Only an idiot would take into consideration his doctorate ...and decades long distinguished career in the field...
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34. aspectre
5:20 PM GMT on May 27, 2008
Thanks, JRRP, for the response in 869 of the last blog. I'm still unfamiliar with (the workings of) the various weather sites, and thus must rely on the kindness of other folks posting those types of maps.

Twas interesting in that the eastern MainDevelopmentRegion and the area surrounding CapeVerde is even farther above the seasonal average I remember from a map posted week or so ago.
Between the unusually high SST

and the low sheer (thanks, weatherblog)

I wouldn't be surprised if the first Atlantic TropicalStorm of the season arises there next week.
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33. weathermanwannabe
11:30 AM CST on May 27, 2008
every planet including our SUN ...The Sun does go through cycles (like sunspots) but it is a "star" not a planet....lol
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32. scottsvb
5:30 PM GMT on May 27, 2008
nogaps has it up by cuba in 108hrs..not disappated...its showing a midlevel circulation forming a new center..though I do think its alittle too far to the east..maybe should be near Isle of Youth.
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31. hurricane23
1:30 PM EDT on May 27, 2008
AWeatherLover here are a few links which may help you understand how (ASCAT) works.

1st link
2nd link
3rd Link
4th Link

Also you were wondering what times the NOGAPS model is released?The NOGAPS model is run four times daily 00Z, 06Z, 12Z, 18Z.
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30. scottsvb
5:27 PM GMT on May 27, 2008
We are in a climate change...but that is normal..every planet including our SUN goes thru cycles!!
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29. moonlightcowboy
12:25 PM CDT on May 27, 2008
Wonderful! Blob fizzles and we move on to the blame of man-made global warming. How typical! Ugh! L8R, no time or preference for this discussion - I guess that's what this is? LOL
Member Since: July 9, 2006 Posts: 184 Comments: 29594
28. Patrap
12:27 PM CDT on May 27, 2008
"Sniff,sniff"

I smell Gasket Smoke....
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27. weatherboykris
5:28 PM GMT on May 27, 2008
12z NOGAPS dissipates the system in 96 hours.
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26. HIEXPRESS
1:20 PM EDT on May 27, 2008
18. MichaelSTL 1:19 PM EDT

Sounds plausible. Do you think there could be a "rebound effect" when something like the PDO switches over after remaining in another mode for so long?
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25. nash28
1:25 PM EDT on May 27, 2008
Dr. Masters and I will just have to agree to disagree on this one.
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24. MississippiWx
5:22 PM GMT on May 27, 2008
21. nash28 5:21 PM GMT on May 27, 2008 Hide this comment.
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.

Oh boy... With all due respect to Dr. Masters, I think it is a little arrogant to blatantly claim that climate change, more specifically destructive climate change is being caused by humans. Not once do I hear anyone state that climate change is cyclical. That before the industrial age the earth has recorded temps that were much warmer than where we are now. No one seems to care about that.


Hey all!

And Nash, I agree with you. Since when has it been a guarantee that we are experiencing human-caused global warming? I wasn't very fond of that statement either.
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23. weathermanwannabe
11:17 AM CST on May 27, 2008
Thanks Dr. M; looks like the shear to the north would inhibit or dissipate any system that may form in that region of the Caribbean according to the general model guidance.......Looks like my beach outing this coming weekend on the Destin beaches will "hold" and the SST's look good enough for a nice long swim in the Florida Gulf (and a few brews afterwards).......Cool Beans
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21. nash28
1:12 PM EDT on May 27, 2008
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.

Oh boy... With all due respect to Dr. Masters, I think it is a little arrogant to blatantly claim that climate change, more specifically destructive climate change is being caused by humans. Not once do I hear anyone state that climate change is cyclical. That before the industrial age the earth has recorded temps that were much warmer than where we are now. No one seems to care about that.
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17. cdo
5:16 PM GMT on May 27, 2008
In NC it will reach a high in the upper 80s might even see some areas hit 90, then come Wed the high will be in the low 70s.
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16. scottsvb
5:17 PM GMT on May 27, 2008
there are outdrafts from clusterd thunderstorms sometimes giving a bouy a reading thinking there is a circulation..but 1 isnt present at this time. 1 may develop tonight into Weds though.
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15. pottery
1:15 PM AST on May 27, 2008
Post 10. Good one.
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14. MocDasters
5:15 PM GMT on May 27, 2008
Our hero Dr. Masters takes a stand and talks about the tropics giving his opinion, will you? You can do it here
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13. Patrap
12:13 PM CDT on May 27, 2008
The Loop In the Jet has brought many a Vigorous system far South this Year.
And that usually always brings the Higher Tornado numbers.
Tough some times Living on 3rd Rock out.
Especially in the Northern Hemisphere and America where we have a unique Setup of Geology and Weather that gives us the Tornado threats.
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12. NOLAinNC
5:10 PM GMT on May 27, 2008
My husband and I were talking about these issues this morning. It's always interesting to hear all the facts, thanks Dr. M. I believe humans are contributing to or even causing rapid climate change, but there are still weather patterns and changes occuring because of natural forces beyond our control.
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11. pottery
1:12 PM AST on May 27, 2008
Thank you Dr.M.
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10. Weather456
1:14 PM AST on May 27, 2008
1438. cchsweatherman 12:58 PM AST on May 27, 2008

While QuikSCAT and ASCAT are rather useless right now....surface obsevervations indicate a circulation is being felt at the surface based on wind shifts...Its weak but its there. However, these observations are not detecting the full extent of the circulation. Products from CIMSS and satellite imagery show its larger than perceived here.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
9. cdo
5:11 PM GMT on May 27, 2008
looks like this blob is a teaser....enough for people to check their "favorites" links and clear out the dead ones.
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8. moonlightcowboy
12:10 PM CDT on May 27, 2008
Much tragedy, ugh. Appreciate the update, Dr. Masters.

20 percent, maybe less with more shear doesn't sound particularly favorable.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
7. scottsvb
5:13 PM GMT on May 27, 2008
There is no closed low in the SW carribean CCHS.. that you see on sat imagery is a midlevel low.
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6. cchsweatherman
1:09 PM EDT on May 27, 2008
Thanks for the update. Will this Tornado season ever slow down and just give everyone a much-neede break, especially in the Midwest and Southeast. Just a horrific year for tornadoes. God bless everyone who has been impacted by the tornadoes this year, especially the victims and their families. As they always say, you can replace property, you can't replace human life.
Member Since: April 14, 2007 Posts: 8 Comments: 5030
4. seflagamma
1:12 PM AST on May 27, 2008
Dr Master's Thank you for the new thread!!!
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3. weatherboykris
5:09 PM GMT on May 27, 2008
Thanks Doctor Masters. Nice blog.
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2. NEwxguy
5:09 PM GMT on May 27, 2008
thanks,Dr. Masters,it has been a violent tornado season.Severe Th storms forming here in New England.
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1. TerraNova
1:08 PM EDT on May 27, 2008
Thanks Doctor!

Link to ASCAT data...we should have a scan of the SW Caribbean on the descending pass sometime this afternoon.
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About JeffMasters

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