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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138. Bamatracker
6:32 PM GMT on May 27, 2008
nws out of new orleans

REGARDING MODEL GENERATION OF TROPICAL LOW FROM WESTERN CARIBBEAN
SEA NEXT WEEK...THE MODELS CONTINUE TO FLIP-FLOP ON THIS SOLUTION
WITH GFS NOW SHOWING SOME ENERGY MEANDERING OVER YUCATAN PENINSULA
WHILE A SEPARATE LOW PEELS OFF AND DEEPENS WHILE MOVING INTO THE
FLORIDA PENINSULA NEXT WEEK. ECMWF SHOWS A SIMILAR SPLIT BUT THEN
DECAYS BOTH CIRCULATIONS RATHER QUICKLY WITH LITTLE FANFARE. THIS
APPEARS TO BE THE START OF A SEASON OF MODEL IDIOSYNCRACIES IN THE
TROPICAL LATITUDES OF THE MODEL DOMAIN. THESE SOLUTIONS...GIVEN
THE DISTANCE IN TIME...ARE BEING DISCOUNTED BEYOND MONDAY.
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137. scottsvb
6:31 PM GMT on May 27, 2008
Latest is there is no closed LLC but there is now a LLVortex near 10N and 80W...could be just that or a starting of a LLC..we wont know until tomorrow morning.
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136. Littleninjagrl
6:32 PM GMT on May 27, 2008
I'm almost scared to post!!! Here goes... this morning (although i didn't catch the whole show) the weather person said there was some "moisture" headed our way - Tampa, fl by Thursday but yet when I look at the forecast for the week it only shows like 10% chance of rain each day. What gives?
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135. Michfan
1:28 PM CDT on May 27, 2008
FFS why did we have to bring GW into this. We had such a good tropical discussion going on. Ugghhhhh. Anyways:

The tropics are heating up nicely.



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134. Bamatracker
6:28 PM GMT on May 27, 2008
quick...run the GFS so we can all watch it instead of all the bickering......
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133. NEwxguy
6:28 PM GMT on May 27, 2008
129. JFV 6:27 PM GMT on May 27, 2008
Good afternoon all! So, what's the latest info on our developing system this afternoon bloggers


Wow,did you come into the wrong blog.
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132. Patrap
1:28 PM CDT on May 27, 2008
Michael,is without a doubt,the Chartmaster of the wunderground.

No one , I mean no one has better source data for the GW debate.

We need to thank him today.
Thanks MichaelSTL.
Member Since: July 3, 2005 Posts: 423 Comments: 127814
131. NEwxguy
6:26 PM GMT on May 27, 2008
125. pottery 6:26 PM GMT on May 27, 2008
Its all a Plot, to keep us all from watching blobs. This GW issue.
Dr. M. throws this out every time he wants one to sneak up on us unawares.
But I'm on to him this time fer sure...........

We all have to fight this subversive plot.
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128. nash28
2:25 PM EDT on May 27, 2008
Jeez.. Some people are so hard-headed... I wonder what it would take to convince you that there is a man-made component... I picture people like you as the kind who are environmental slobs, trashing the environment in every way they possibly can, just for the fun of it.

Dude, that was a pretty baseless attack.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
127. getalife
6:23 PM GMT on May 27, 2008
Hey Michael, how about we just outlaw CO2 completely?? Seeing that it is a "pollutant" now. lol How would mankind fare then???
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126. NEwxguy
6:24 PM GMT on May 27, 2008
And don't forget the wonderful TV GW discussion series LOST
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125. pottery
2:21 PM AST on May 27, 2008
Its all a Plot, to keep us all from watching blobs. This GW issue.
Dr. M. throws this out every time he wants one to sneak up on us unawares.
But I'm on to him this time fer sure...........
Member Since: Posts: Comments:
121. EvPv
6:23 PM GMT on May 27, 2008
On Dr. Masters statement, while I've grown to agree with him over the last few years, he could have made the statement differently, but then again, forget evolution... it hasn't been proven so therefore go with intelligent design...not.

Evolution took a long time for it's changes to show but it doesn't mean it did not happen.

Anyway, for the climate change doubters, forget the topic and look at how many U.S. lives have been lost fighting for & protecting oil interests.

If I'm right or wrong, everything comes down in our lives to the choices we make.
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120. Patrap
1:24 PM CDT on May 27, 2008
Bye..floss after every Model run,..er meal.
Member Since: July 3, 2005 Posts: 423 Comments: 127814
119. cchsweatherman
2:18 PM EDT on May 27, 2008
You know what, I'll speak with you all later this evening when we HOPEFULLY will have sanity and calm restored to the blogs. Can't stand this constant bickering back and forth on global warming. Have a nice day and I hope you all realize how immature you all appear arguing about something that you all agree nobody has an answer to. That's exactly why they call global warming a phenomena.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
118. KrazyKaneLove
6:22 PM GMT on May 27, 2008
My favorite global warming dessert..Baked Alaska
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117. nash28
2:22 PM EDT on May 27, 2008
How much carbon dioxide per square mile is converted to Oxygen in a rain forest

That question alone oughta make people stop and think about the basic science.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
114. nash28
2:19 PM EDT on May 27, 2008
And on a more sobering note, those pics of devastation are horrible.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
113. captainhunter
6:16 PM GMT on May 27, 2008
Hey NEwxguy... Don't forget "Swirls gone Wild" and "The Blob".
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111. tornadofan
6:15 PM GMT on May 27, 2008
Here is a question for everyone and I want to see a response from everyone. Why the hell are you all arguing about something that you all agree nobody has the answer to? Just want to know.

If we all had the answer, it would be to hard to argue.

Gulfscotsman - we do damage the earth, much the same way a person damages himself from eating too much or smoking. Earth can definitely heal itself.
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110. Patrap
1:16 PM CDT on May 27, 2008
Psst,,check the Artic Ice Imagery..
Member Since: July 3, 2005 Posts: 423 Comments: 127814
108. nash28
2:13 PM EDT on May 27, 2008
Most climate scientists who know much more than anybody on this blog would disagree with that statement, and yes, they have looked into every possibility; that is how science works; if something can be explained this way but not that way then the first must be true, unless proven otherwise

STL- You're a smart guy, but MAN! Did you REALLY just say this??? So..... They have looked into every possibility??? Settled science? Of course it is explained one way and not the other!!! DUH!! The damn grants and FUNDS would dry up faster than Gore's political career if it were any different! Wow!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
107. Patrap
1:15 PM CDT on May 27, 2008
ABC news:

Expert Explains High Number of Tornadoes
Active Winter Storms Lead to Many Twisters Link
Member Since: July 3, 2005 Posts: 423 Comments: 127814
106. NEwxguy
6:05 PM GMT on May 27, 2008
Global Warming Movies

Gone with the WIND
RAINman
A Raisin in the SUN
HAIL to the chief
Blue THUNDER
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105. getalife
6:14 PM GMT on May 27, 2008
104 good one Pat, lol
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104. Patrap
1:11 PM CDT on May 27, 2008
Maybe we should all getalife..LOL
Member Since: July 3, 2005 Posts: 423 Comments: 127814
103. nash28
2:10 PM EDT on May 27, 2008
My question is what do you contribute to MANY scientists saying we are entering a mini ice age? What is the explanation there? Global Warming taking a nap?
Member Since: July 11, 2005 Posts: 190 Comments: 16972
102. pottery
2:05 PM AST on May 27, 2008
Bravo Gulf.
And the sooner the better too, I say.
But now, we want to go to Mars, then....... ?
We are a virus no doubt, and sooner or later the host will fight back and cure itself.

I'm thinking of setting up a religion, any ideas ?
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98. TerraNova
2:06 PM EDT on May 27, 2008
Why do scatterometers always have to miss the area which we are most interested in? The new ASCAT pass left a hole in the SW Caribbean...still, it shows winds blowing from the south on the eastern portion of the blob north of Panama (northwest of 10N, -75W). This pass shows an elongated circulation just south of 10N, -90W. Hopefully we'll have the QS up soon.

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95. Patrap
1:07 PM CDT on May 27, 2008
Not Quite V-8 combustion,but not unlike a Hot-Pocket snack, too.
Member Since: July 3, 2005 Posts: 423 Comments: 127814
94. KrazyKaneLove
6:05 PM GMT on May 27, 2008
NP Nash, (looking over shoulder and whispering..),I actually agree with you on the global warming issue.
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92. nash28
2:06 PM EDT on May 27, 2008
GS- THANK YOU for what has to be the most sensible statement on the matter that I have heard in a long time!!!

The Earth will still be here folks, just like it was before we were here. We are a tick, a flea if you will on the Earth's back. She can shake us off in a blink.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
90. cchsweatherman
2:03 PM EDT on May 27, 2008
Here is a question for everyone and I want to see a response from everyone. Why the hell are you all arguing about something that you all agree nobody has the answer to? Just want to know.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
88. Patrap
1:04 PM CDT on May 27, 2008
1305 CST Back to class.

A hurricane's "hot towers" can increase its intensity by adding power to boost the storm's heat engine. For the first time, research meteorologists have run complex simulations of these phenomena using a very fine temporal resolution. They have combined this new simulation data with satellite observations to study the innerworking of the "hot towers" in never-before-seen detail. Link
Member Since: July 3, 2005 Posts: 423 Comments: 127814

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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.

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