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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838. Drakoen
2:07 AM GMT on May 28, 2008
826. Weather456 2:04 AM GMT on May 28, 2008
Sorry my post should say southwest....not southeast.


How? moving from 90W to 88.7W is east movement.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
837. kmanislander
2:08 AM GMT on May 28, 2008
Nope, definitely the "old" JP !~

welcome back JP
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835. FLWeatherFreak91
10:07 PM EDT on May 27, 2008
Maybe it's because I have been looking at this screen all day long but, it seems to me that 90E is less linear now and more consolidated. Organizing?
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834. kmanislander
2:07 AM GMT on May 28, 2008
Absolutely Nash !

Go to the top of the class !!
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832. CaneAddict
2:03 AM GMT on May 28, 2008
821. Weather456 2:02 AM GMT on May 28, 2008
jphurricane2006,

I've been reading ur post for the past days now and I cudnt help but notice that u have change. I am not seeing the same Jp from 2006 and 2007. U sort of like another "eye".


Exactly.
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831. nash28
2:04 AM GMT on May 28, 2008
Ok, so the Low, which was hailed THE LOW earlier by everyone and their mother is moving S, SSS, SSE, SESE, ESE, EESE, ESSSSEE, or not at all...

Does that about sum up what I have missed this evening?

:-)
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830. kmanislander
2:06 AM GMT on May 28, 2008
You mean JP is not JP ??
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829. weatherblog
2:03 AM GMT on May 28, 2008
812. Weather456 1:59 AM GMT on May 28, 2008
Tracking 90E's movement...movement over 6 hrs is
southeast


200805280000 9.8 -88.7 25
200805271800 10 -90 25


That changes a lot...lmao
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828. extreme236
2:05 AM GMT on May 28, 2008
In case any of the new people here don't know who 456 is referring to is "eye" who as nash, drak, and other's know is my dearest blog friend lol
Member Since: August 2, 2007 Posts: 19 Comments: 19234
827. Drakoen
2:03 AM GMT on May 28, 2008
821. Weather456 2:02 AM GMT on May 28, 2008
jphurricane2006,

I've been reading ur post for the past days now and I cudnt help but notice that u have change. I am not seeing the same Jp from 2006 and 2007. U sort of like another "eye"
.

Without instigating anything, thats the same thing I noticed. I was actually about to say something about that. Its kind of been bothering me.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
825. extreme236
2:03 AM GMT on May 28, 2008
I think its certainly clear what the NHC is thinking on this system just based upon their sfc maps.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
823. CaneAddict
1:52 AM GMT on May 28, 2008
780. Michaael 1:42 AM GMT on May 28, 2008
Be nice to get some tropical rains here in TX but if its a major, heck no, go east to....well.... Florida


You know it takes ALOT for me to add someone to my ignore list. Michaael has tooking the first spot on the list.
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822. Drakoen
2:02 AM GMT on May 28, 2008
Guys this is not rocket science. Use RAMSDIS tracking and use satellite loop.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
821. Weather456
9:59 PM AST on May 27, 2008
jphurricane2006,

I've been reading ur post for the past days now and I cudnt help but notice that u have change. I am not seeing the same Jp from 2006 and 2007. U sort of like another "eye".
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819. JLPR
9:58 PM AST on Mayo 27, 2008
810. Michaael 9:56 PM AST on Mayo 27, 2008
802. JFV 8:54 PM CDT on May 27, 2008
I totally agree with you there Extreme! clearly 90l is in it's developing stages!

Sounds like that is what you want so it'll hit Florida dude.


That would be good. no? Inst south Florida on a
drought? a nice, wet, weak tropical storm with winds below 45mph would actually be good for that area =).
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818. kmanislander
2:01 AM GMT on May 28, 2008
I will settle for East or just S of due East
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817. weatherblog
1:58 AM GMT on May 28, 2008
805. Weather456 1:55 AM GMT on May 28, 2008
Tracking 90E's movement...movement over 6 hrs is southwest


200805280000 9.8 -88.7 25
200805271800 10 -90 25


LOL that's completely the oppisite direction we've been dscussing it's going in. But it's hard to say since the convection may be fooling many of us... including me.
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815. kmanislander
1:59 AM GMT on May 28, 2008
Or South East LOL
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814. Drakoen
1:59 AM GMT on May 28, 2008
Kman its moving slowly just south of due east.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
811. kmanislander
1:57 AM GMT on May 28, 2008
Hi Nash

Right now the question is whether 90E is moving East, South West or not moving at all

There you go !
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809. taco2me61
1:53 AM GMT on May 28, 2008
Hi Y'all,
Just checking in and see what is going on with the possible invest in the caribbean.....
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808. extreme236
1:53 AM GMT on May 28, 2008
NHC shows both lows in 24 hours then gets rid of 90E at 72 hours and shows the Caribbean low in the Gulf of Honduras...the NHC apparently prefers the GFS solution at this point.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
807. nash28
1:55 AM GMT on May 28, 2008
Whew.... Ok, no more errands. Been going since 5am. So, what's happening?
Member Since: July 11, 2005 Posts: 190 Comments: 16972
806. weatherblog
1:50 AM GMT on May 28, 2008
795. jphurricane2006 1:50 AM GMT on May 28, 2008
wow guys lol


the low is in the same spot guys, it is stationary folks

did someone say 3 knots? um 3 knots is stationary lol


I'm just saying what I'm seeing based on watching loops of 90E. But, it just seems to recently have started a faster pace to the east. Maybe to 5 knts? LOL

Anyways, even if the low is not moving very fast, the convection with the system looks to be moving in a fast general direction towards Panama....It's ok if we disagree. I could be wrong.
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805. Weather456
9:41 PM AST on May 27, 2008
.
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804. moonlightcowboy
8:53 PM CDT on May 27, 2008
A good chunk of this convection is ITCZ convergence.

Member Since: July 9, 2006 Posts: 184 Comments: 29610
803. Tazmanian
6:53 PM PDT on May 27, 2008
thanks nrtiwlnvragn looks like some one new what i was talking about thanks
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801. Drakoen
1:50 AM GMT on May 28, 2008
The low in the EPAC is moving to the east.
Member Since: October 28, 2006 Posts: 57 Comments: 30727
800. moonlightcowboy
8:51 PM CDT on May 27, 2008
Member Since: July 9, 2006 Posts: 184 Comments: 29610
799. kmanislander
1:51 AM GMT on May 28, 2008
JP

If the low is stationary then the upper levels of the system have left it behind
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798. extreme236
1:50 AM GMT on May 28, 2008
Well if you want to get technical JP its moving at 3mph lol, so its close to stationary :-)
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797. atmoaggie
1:49 AM GMT on May 28, 2008
Me too...later all.
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796. weatherblog
1:48 AM GMT on May 28, 2008
*786

Wow! That shear certainly makes up for the above average shear in the Caribbean. lol
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794. rareaire
1:49 AM GMT on May 28, 2008
good night storm, thanks as always
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793. nrtiwlnvragn
9:48 PM EDT on May 27, 2008
Taz

Here's the Link, but 90E is not on the plot. I think they only plot Atlantic storms.
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792. pearlandaggie
1:47 AM GMT on May 28, 2008
i'm out, folks! have a good evening....enjoyed it!
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789. extreme236
1:46 AM GMT on May 28, 2008
What I'm seeing is that we have a developing sfc low in the Caribbean and 90E and it is moving in the Caribbean low's direction and the GFS was forecasting the two to merge in the Caribbean and it seems that it could be correct.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
788. kmanislander
1:44 AM GMT on May 28, 2008
90E certainly appears to be moving East at quite a clip. If not there would have to be a serious decoupling of the low and mid to upper level circulations and there is nothing to suggest that has occurred
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.