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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1035. moonlightcowboy
2:09 AM CDT on May 28, 2008
JFL, some, I think - I'm not in that yet, though. (lol, as if it mattered); but, right now, it looks stationary to me and getting more organized. There's still too much shear in the Caribbean to support further development.
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1033. moonlightcowboy
2:03 AM CDT on May 28, 2008
RGB loop of 90E

Definitely good rotation. Seems to be more stationary.
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1032. KoritheMan
6:52 AM GMT on May 28, 2008
Just looked at the latest model runs and a lot of them appear to be forecasting a weaker system. Still, as was stated numerous times last year, until the models have a good handle on a system, it's still anybody's guess. A lot of the models are also keeping the storm in the Pacific. Regardless of the basin though, and whether or not tropical cyclogenesis occurs, portions of Central America are going to see heavy rains from this system.
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1031. 7544
6:09 AM GMT on May 28, 2008
hi carb. is just about to do its thing and whats around 60w 25n hmmmm could this one be first is the race on
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1030. StormJunkie
5:49 AM GMT on May 28, 2008
I see there was some ruckus and deleted posts mlc....lol

Bling Bling on Mars!

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1029. moonlightcowboy
12:43 AM CDT on May 28, 2008
SJ, yeah, it's out and a lil high, huh? If the TUTT leaves it behind then it could be something. 90E's been the hullaballou today!
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1028. weatherboykris
5:43 AM GMT on May 28, 2008
NOGAPS almost done.
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1027. KEEPEROFTHEGATE (Mod)
1:37 AM EDT on May 28, 2008
yep lets watch an see
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1026. StormJunkie
5:35 AM GMT on May 28, 2008
Looks like a TUTT or something to the left of my image. That thing is smack dab in the middle of the Atl.
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1025. KEEPEROFTHEGATE (Mod)
1:32 AM EDT on May 28, 2008
90e
your shot that just startin to pop not sure what it is its movin westward a little
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1024. moonlightcowboy
12:32 AM CDT on May 28, 2008
I'm pickin' on the "explode" part; but, "yes" good-eye. That twave may be just what cranks it up!
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1023. StormJunkie
5:28 AM GMT on May 28, 2008
I am confused, what is about to explode? 90e or this...



!~)
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1022. KEEPEROFTHEGATE (Mod)
1:23 AM EDT on May 28, 2008
another witness for the awakening
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1021. moonlightcowboy
12:21 AM CDT on May 28, 2008
Hey, SJ and g'morning! Dayum tropics are about to explode and you've not even been around!!! It's all your fault! Dadgummit!
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1020. StormJunkie
5:17 AM GMT on May 28, 2008
Morning all :~)

Or anyone that is still up! What's the latest?
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1019. Beachfoxx
12:15 AM CDT on May 28, 2008
Wow...

I am speechless. It is morphing...
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1018. Weather456
12:50 AM AST on May 28, 2008
00Z tracks
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1017. moonlightcowboy
11:54 PM CDT on May 27, 2008
Yep, Keeper - comin' alive!
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1016. RyanFSU
12:47 AM EDT on May 28, 2008
00Z HWRF is much less impressive than the 18Z run, with slow development to a strong tropical storm/marginal hurricane just prior to landfall -- remaining on the Eastern Pacific side. Rest of the forecast will take another hour or so to finish integrating on the Weather Bureau's supercomputer...


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1015. KEEPEROFTHEGATE (Mod)
12:39 AM EDT on May 28, 2008
the awakening
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1014. moonlightcowboy
11:40 PM CDT on May 27, 2008
Photobucket

LATEST SURFACE MAP
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1013. KoritheMan
4:36 AM GMT on May 28, 2008
I noted in my blog entry eariler that I thought it had a shot to become a tropical depression. But I didn't expect THIS much of an organization spurt tonight. Geez.
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1012. Beachfoxx
11:30 PM CDT on May 27, 2008
W456
Its going to be interesting to see how it goes.

Great info here tonight!

Thanks to all!

Peace!
Member Since: July 10, 2005 Posts: 157 Comments: 29385
1011. Weather456
12:24 AM AST on May 28, 2008
I dont think it shud make a difference which side it forms on if it has the potential to affect our frends over at Central America.
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1010. Beachfoxx
11:25 PM CDT on May 27, 2008
Divine? maybe? LOL

We could use the rain from a system, but I sure hate to see the season start so soon... Hopefully, shear will steer it towards FL and keep it a "rainmaker".
Member Since: July 10, 2005 Posts: 157 Comments: 29385
1009. weatherblog
4:26 AM GMT on May 28, 2008
Good night!
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1008. weatherblog
4:25 AM GMT on May 28, 2008
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1006. weatherboykris
4:22 AM GMT on May 28, 2008
Indeed 456, we'll likely have EPAC TD-1 tomorrow morning.
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1005. moonlightcowboy
11:21 PM CDT on May 27, 2008
BFox, no, your avatar is just devine! ; P
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1004. weatherblog
4:18 AM GMT on May 28, 2008
Quick update on my blog here. My thoughts on what's happening in the tropics is there. Thanks!
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1003. moonlightcowboy
11:20 PM CDT on May 27, 2008
Yeah, 456, I looked at that last twave a bit ago, riding quite high.
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1002. Weather456
12:20 AM AST on May 28, 2008
90E looks impressive

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1001. Beachfoxx
11:20 PM CDT on May 27, 2008
Cowboy! Nice Avatar!
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1000. Beachfoxx
11:18 PM CDT on May 27, 2008
Interesting.... Could we have Arthur before the official start of H - Season??

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999. Weather456
12:15 AM AST on May 28, 2008
Also, our tropical waves are not confined to south of 10N, I notice the AEJ axis is now along 10N meaning the center of the wave axis will along 10N and the waves will most likely be south of 15N. For example the new wave and the wave entering the ECARIB.
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998. moonlightcowboy
11:15 PM CDT on May 27, 2008
994. Weather456 11:09 PM CDT on May 27, 2008
Based on the shear forecast the chances of 90L in the Western Caribbean are slim but still watchin the coast of africa.


Yep, and yep! 456, I'm still thinking we're gonna see that invest pop there before we all think it would normally.
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997. franck
4:16 AM GMT on May 28, 2008
TexasGulf...true, shear conditions in GOM seem to be reestablishing 2-3 days out.
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996. TexasGulf
4:02 AM GMT on May 28, 2008
I will congratulate all believers in 90E. Your predictions and best wishes for its health are rewarded.

I hope it does move North into the Gulf. It won't find a friendly environment for strengthening, but we can sure use the rain in South Texas.
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995. TampaSpin
12:07 AM EDT on May 28, 2008
There is an ULL that will be a player in preventing favorable upper levels for development.
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994. Weather456
12:05 AM AST on May 28, 2008
989. JFV 12:02 AM AST on May 28, 2008
Well Weather, since partically everything has been safely confirmed already, when are you expecting it to become a invest or depression? And later down the road there I say TS perhaps? your thoughts sir?


Just like with the prediction with EPAC invest, if the disturbance gets better organize and continues to perist offshore and enviromental conditions improve, we should see 90L in 72 hrs time. Based on the shear forecast the chances of 90L in the Western Caribbean are slim but still watchin the coast of africa.

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993. TampaSpin
12:03 AM EDT on May 28, 2008
JFV i personally don't think much can develop until the sheer relaxes and that does not seem to be happening soon in the short term that i can see.
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992. weatherboykris
4:04 AM GMT on May 28, 2008
989. JFV 4:02 AM GMT on May 28, 2008
Well Weather, since partically everything has been safely confirmed already, when are you expecting it to become a invest or depression? And later down the road there I say TS perhaps? your thoughts sir?


What, specifically, has been safely confirmed? Not to stir the pot, but we don't even have a confirmed closed low yet. Yes, I do believe we will see Arthur before this week is out, but it still very much wait and see at this point. Alot needs to happen, and could go wrong.
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991. weatherboykris
4:03 AM GMT on May 28, 2008
Hey guys! Interesting discussion there, 456!
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988. Weather456
11:57 PM AST on May 27, 2008
984. JFV 11:55 PM AST on May 27, 2008
WOW, Weather did that discussion just absically confirmed that a tropical cyclone will indeed form in the carib within the next few days? If I just read it correctly that is!


Not predicting a tropical cyclone on the Caribbean but rather the surface low being forecast by models (TD status likely). Also any development will be slow to occur until the upper anticyclone forms and not much will develop before it begins to interact with central america. But there are now two surface lows in either basin with 90E the more organize and more likely to develop.
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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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