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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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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787. Tazmanian
6:37 PM PDT on May 27, 2008
looks like i this have to show you LOL


can i have a linke to this site thank you


lol
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786. atmoaggie
1:44 AM GMT on May 28, 2008
Back to the shear. Can you guess where the shear, on average, has recently dropped way below climatology?

Correct (sure), the GoM:

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785. pearlandaggie
1:45 AM GMT on May 28, 2008
LMFAO, AtmoAggie! now you're making me rethink that order! ;)
Member Since: September 14, 2007 Posts: 3 Comments: 3963
783. weatherblog
1:41 AM GMT on May 28, 2008
777. jphurricane2006 1:41 AM GMT on May 28, 2008
its not moving east, it is stationary


Maybe the low itself... but looking at infrared loops etc, a lot of the convection is heading towards the west coast of Panama. Just a simple observation.
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782. extreme236
1:42 AM GMT on May 28, 2008
well JP according to the NHC model page, it is moving slowly east at 3 knots
Member Since: August 2, 2007 Posts: 19 Comments: 19234
781. pearlandaggie
1:42 AM GMT on May 28, 2008
LMFAO, AtmoAggie! now you're making me rethink that order! ;)
Member Since: September 14, 2007 Posts: 3 Comments: 3963
779. Weather456
9:39 PM AST on May 27, 2008
We just had a breif passing shower in St. Kitts helping to break our recent dry spell...thanks to that tropical wave and the moisture invading from the SW.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
778. atmoaggie
1:38 AM GMT on May 28, 2008
atmo, i'm putting in an order for climatologically abnormally high levels of wind shear for the entire season...when do you think you can deliver my order?

You want fries with that?

Warning, these orders are filled as correctly and promptly are they are at the Bryan Kettle during the night shift.
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776. weatherblog
1:37 AM GMT on May 28, 2008
*761

It looks like 90E is moving quickly to the east. By tomorrow, it could even hit Panama and enter the SW Caribbean if it keeps that pace/direction up. Wouldn't be suprised either.
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774. atmoaggie
1:30 AM GMT on May 28, 2008
Good, extreme. Been far too busy for the blog most of the day. Looking into hourly updating a display system with ship obs.

I found more than 200/hour at the usual 6s (0,6,12,18). These will not be in a cat4, obviously (unless someone REALLY had a charlie foxtrot), but could be intersting. Some of the ship obs are in places where we do not have many buoys...Bahamas, BOC(1), WCarib(1). Already have code to digest, error check, and plot buoys, including drifters...should be a snap.

Also building a system to digest MODIS oceanic chlorophyll and another system to build an hourly wave height analysis field from obs and the WaveWatch for a background.

Like I said busy.

I see the GFS is showing us a drunk TD, stumbling about...how nice.
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772. FLWeatherFreak91
9:37 PM EDT on May 27, 2008
That's weird. For most of the season the shear has been waay below average, but right when the models start predicting development, the shear shoots up.

....It's the government... don't tell any one lol
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771. weathersp
9:35 PM EDT on May 27, 2008
Use the Magic and Buttons please!
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770. Weather456
9:32 PM AST on May 27, 2008
Posted this in my blog this morning:

The 00Z and 06Z model runs show development of the Eastern Pacific area in the next day or two and develops a weaker low pressure around the Gulf of Honduras (Western Caribbean) that moves into the Yucatan and Bay of Campeche later this weekend as the disturbance moves north from the SW Caribbean Sea. It is rather unusual to have development taking place in both basins but the consensus is that. However, until the disturbance becomes more define, we can’t really give much confidence in the track.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
769. weatherblog
1:33 AM GMT on May 28, 2008
*758

That's weird. For most of the season the shear has been waay below average, but right when the models start predicting development, the shear shoots up.
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768. weathersp
9:28 PM EDT on May 27, 2008
I am glad they named it an invest so they could get the extra model support of like the GFDL and the HWRF.

HWRF has a loose wire in there I think as it has a Cat 2 hurricane into the Costa Rica Western Coast line.
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766. pearlandaggie
1:33 AM GMT on May 28, 2008
patrap, i see what you did there.....
Member Since: September 14, 2007 Posts: 3 Comments: 3963
765. weatherblog
1:31 AM GMT on May 28, 2008
759. FLWeatherFreak91 1:31 AM GMT on May 28, 2008
Ok everyone who already hasn't HIDE michaael... i hid him ten minutes ago and i still see his posts bc you all keep quoting them lol. If you just hide him them we don't have to worry about him.


Sorry for quoting him...he's now on my ignore list. lol
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764. Patrap
8:32 PM CDT on May 27, 2008
Hide and Seek?

Thats different...
Member Since: July 3, 2005 Posts: 423 Comments: 127803
763. pearlandaggie
1:30 AM GMT on May 28, 2008
atmo, i'm putting in an order for climatologically abnormally high levels of wind shear for the entire season...when do you think you can deliver my order?
Member Since: September 14, 2007 Posts: 3 Comments: 3963
761. moonlightcowboy
8:28 PM CDT on May 27, 2008
East Pacific IR LOOP
Member Since: July 9, 2006 Posts: 184 Comments: 29596
760. rareaire
1:24 AM GMT on May 28, 2008
im a cat adjuster and even I dont want a hurricane to hit anywhere. I you ever been thru one or assisted in the aftermath you wouldn't either. I like my Hail storms , Steady work and nobody gets hurt.....
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759. FLWeatherFreak91
9:30 PM EDT on May 27, 2008
Ok everyone who already hasn't HIDE michaael... i hid him ten minutes ago and i still see his posts bc you all keep quoting them lol. If you just hide him them we don't have to worry about him.
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758. atmoaggie
1:26 AM GMT on May 28, 2008
Shear is supposed to relax here soon.

The average over the Caribbean has been only rising over the last couple of days. Now higher than climatology.

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756. extreme236
1:29 AM GMT on May 28, 2008
Hey atmoaggie, how are you doing today?
Member Since: August 2, 2007 Posts: 19 Comments: 19234
754. Tazmanian
6:27 PM PDT on May 27, 2008
oh has the mode map page for 90E ???


you no when evere we get 90L we get some mode runs map can any one post me the link


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753. weatherblog
1:26 AM GMT on May 28, 2008
744. Michaael 1:25 AM GMT on May 28, 2008
Do you want to pay $7 a gallon a gas?? because you will if LA or TX get hit.


You don't seem to understand...nobody wants TX, LA, or FL to get hit. The hurricanes will hit where they want to hit. There's no stopping that. You don't control the hurricanes.
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752. pearlandaggie
1:27 AM GMT on May 28, 2008
hey shawn...nice seeing ya!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
750. pearlandaggie
1:26 AM GMT on May 28, 2008
howdy back at ya!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
749. OUSHAWN
1:26 AM GMT on May 28, 2008
Hey PEARLAND!!! I'm in Clear Lake...use to live in Pearland...Go Oilers!

Anyway, first post of the year! Looks like things are getting interesting!

Shawn
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748. extreme236
1:26 AM GMT on May 28, 2008
Maybe Taz
Member Since: August 2, 2007 Posts: 19 Comments: 19234
747. nrtiwlnvragn
9:23 PM EDT on May 27, 2008
Anyone have spaghetti plots from the 00Z update? I've only found them on WU, but would like to see some of the other models.
Member Since: September 23, 2005 Posts: 14 Comments: 11027
746. atmoaggie
1:21 AM GMT on May 28, 2008
Some trolls show up just to be quoted. It makes them feel special and loved.

If you do not want to use the html ignore button, use the mental one. If you feed it, it will never leave. If no one responds, trolls get bored and go play video games.

Howdy, pearland ag, stormw, extreme, pat, terra, 23, 456, 789, and anyone or any number I missed.
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745. Tazmanian
6:24 PM PDT on May 27, 2008
so sould 90E be 90E/90L???
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743. zoomiami
1:24 AM GMT on May 28, 2008
Thanks Storm - always like your updates - plain english!

As a reminder - please don't paste in the comments of the trolls - it defeats the purpose for those of us who use the magic button.

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742. Tazmanian
6:22 PM PDT on May 27, 2008
oh has the mode map page for 90E???
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741. extreme236
1:22 AM GMT on May 28, 2008
The 2100 UTC vorticity map seems to suggest a very broad low pressure extending from 90E into the south Caribbean.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
740. weatherblog
1:18 AM GMT on May 28, 2008
709. Michaael 1:06 AM GMT on May 28, 2008
Im not wishing on anybody. Im just saying if there is a big one, Florida has to take it, simple as that. I mean come on, what's in Florida besides retirees and mickey mouse runnin around, and people from FL always model watching when there aint nothing there!


Wow, this is so scripted and fake what you just said saying people in Florida don't matter. Get real. This is the perfect way (and you know it) to get the blog in an argument. You've probably been banned many times, and you're back for more. Hate people like you...
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738. Tazmanian
6:20 PM PDT on May 27, 2008
when could we see 90L????
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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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