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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538. Michfan
6:08 PM CDT on May 27, 2008
Looks like QScat got fixed.
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537. IKE
6:08 PM CDT on May 27, 2008
533. moonlightcowboy 6:08 PM CDT on May 27, 2008
Dr. Masters has pretty much ruled out any Caribbean development already.


According to the latest GFS and NOGAPS run, he may have a different feeling about it tomorrow.
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536. moonlightcowboy
6:08 PM CDT on May 27, 2008
534. LMAO, Pat - that's about as accurate as something crossing over from the Pacific and developing in all that shear, dry air and high pressure to the north.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
535. SpaceThrilla1207
11:06 PM GMT on May 27, 2008
I don't think the EPAC system (90E) has that much of a chance of developing in the EPAC, although dry air is not a factor wind shear is going up and the system will probably track over land before anything signifigant forms.

My guess is that the GFS and NOGAPS will prove to be right and 90L will cross Central America before developing and join with our Caribbean system, which might spell some trouble for the caribbean down the road.
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534. Patrap
6:07 PM CDT on May 27, 2008
I think maybe the Caribbean feature is a 07 Karen Remnant.
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533. moonlightcowboy
6:07 PM CDT on May 27, 2008
Dr. Masters has pretty much ruled out any Caribbean development already.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
532. nash28
11:07 PM GMT on May 27, 2008
Hang on gang. Gotta get the chicken on the grill..
Member Since: July 11, 2005 Posts: 190 Comments: 16972
531. Michfan
6:06 PM CDT on May 27, 2008
Yeah i see what you mean now Drak. Looks like 90E will get hung out to dry if it does meander to the SW Caribbean.
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530. nash28
11:06 PM GMT on May 27, 2008
Also in referrence to why and how Barry formed and survived.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
529. IKE
6:05 PM CDT on May 27, 2008
Kind of looks like the Caribbean low is going to take over....eventually.
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528. Drakoen
11:05 PM GMT on May 27, 2008
We might not have any development in either basin the way these models are going lol.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
527. sporteguy03
11:03 PM GMT on May 27, 2008
Nash,
Pretty much where is the model link?
The system will be in the EPC not Carib
some sat pics and I told you so's
about it and a Mars pic from Patrap.
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526. moonlightcowboy
6:04 PM CDT on May 27, 2008


20 kts (plus) shear in the Caribbean, except for the extreme swCarib.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
525. nash28
11:04 PM GMT on May 27, 2008
I believe I mentioned this ULH in earlier posts as to why I saw development occuring for the CB system in time...
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524. Drakoen
11:01 PM GMT on May 27, 2008
519. Michfan 11:01 PM GMT on May 27, 2008
Looks like that Upper Level high may help both systems develop short term with one absorbing the other. Interesting turn of events this evening.


It can't help both. Its either one or the other and right now that upper level high is headed into the Southwest Caribbean.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
523. IKE
6:00 PM CDT on May 27, 2008
NOGAPS has it on the coast of Belize in 72 hours....appears in line with the latest GFS run...a general WNW direction for the next 3 days.
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522. Drakoen
11:01 PM GMT on May 27, 2008
Steering currents will be very weak throughout most of the Caribbean.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
521. Patrap
6:00 PM CDT on May 27, 2008
Not much nash.

Nice Mars pics though.
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520. stormhank
11:01 PM GMT on May 27, 2008
Link for those interested heres a good site to get great tropical weather info.
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519. Michfan
5:57 PM CDT on May 27, 2008
Looks like that Upper Level high may help both systems develop short term with one absorbing the other. Interesting turn of events this evening.
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518. moonlightcowboy
6:00 PM CDT on May 27, 2008


700-850mb steering layer
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516. IKE
5:59 PM CDT on May 27, 2008
508. stormhank 5:56 PM CDT on May 27, 2008
mail ike


Mail back at you.
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515. nash28
10:58 PM GMT on May 27, 2008
Home from work pulling out the grill.

What have I missed in the last 134 or so posts:-)
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514. plywoodstatenative
10:58 PM GMT on May 27, 2008
well as odd as the past couple of seasons has been, I would not discount anything.
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513. Drakoen
10:57 PM GMT on May 27, 2008
510. stormhank 10:56 PM GMT on May 27, 2008
hey drak.. do you know when they will begin GFDL runs on 90E?


I don't know if the GFDL or HWRF will be run but if it is it would probably come out later in the evening. Perhaps after the NOGAPS 18z run.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
511. Drakoen
10:55 PM GMT on May 27, 2008
A nice loop of both systems is on the old RAMSDIS site.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
510. stormhank
10:56 PM GMT on May 27, 2008
hey drak.. do you know when they will begin GFDL runs on 90E?
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509. moonlightcowboy
5:53 PM CDT on May 27, 2008


Tropic-wide 850mb vorticity
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508. stormhank
10:55 PM GMT on May 27, 2008
mail ike
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507. extreme236
10:54 PM GMT on May 27, 2008
506. Drakoen 10:52 PM GMT on May 27, 2008
2100 UTC Cimss shear map shows the upper level high is now over central Panama.


Yep...seems conditions may be gradually improving for development down there.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
506. Drakoen
10:51 PM GMT on May 27, 2008
2100 UTC Cimss shear map shows the upper level high is now over central Panama.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
505. Patrap
5:47 PM CDT on May 27, 2008
Another View.



The image from the High Resolution Imaging Science Experiment (HiRISE) on NASA's Mars Reconnaissance Orbiter marks the first time ever one spacecraft has photographed another one in the act of landing on Mars.

Meanwhile, scientists pored over initial images from Phoenix, the first ever taken from the surface of Mars' polar regions. Phoenix returned information that it was in good health after its first night on Mars, and the Phoenix team sent the spacecraft its to-do list for the day.


Imagery can be found here at the Phoenix NASA Home page.Link
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504. IKE
5:46 PM CDT on May 27, 2008
NOGAPS is going WNW on it's latest run...which is out through 48 hours...that's in line with the GFS.
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503. stormhank
10:44 PM GMT on May 27, 2008
does anyone know when the GFDL will begin model runs on 90E?
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502. surfmom
10:44 PM GMT on May 27, 2008
Patrap - you always have the picture i want to see LOL. I heard about that photo and figure I wouldn't get to see it --thanks! BBl
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501. IKE
5:44 PM CDT on May 27, 2008
This system may be around somewhere a week from now..maybe longer.....
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500. moonlightcowboy
5:44 PM CDT on May 27, 2008
CIMSS site his apparently having some trouble with obs and invest location, etc...still working the kinks out, too.
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499. Drakoen
10:44 PM GMT on May 27, 2008
NOGAPS has the system moving north in the Caribbean east of Nicaragua.
Member Since: October 28, 2006 Posts: 57 Comments: 30490
498. TEXASYANKEE43
10:40 PM GMT on May 27, 2008
Here is NOGAPS

http://www.bvipirate.com/NOGAPS.phtml
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497. surfmom
10:39 PM GMT on May 27, 2008
Aloha StormW - good to see you, looks like a possible wave maker for the gomex... that would be nice! Not looking for a "STORM OF MASS DESTRUCTION"
just a wave maker and bringer of rain to SWFL.

Kitchen is calling BBL
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496. IKE
5:40 PM CDT on May 27, 2008
Here's the NOGAPS.....

Link
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495. Patrap
5:39 PM CDT on May 27, 2008
Camera on Mars Orbiter Snaps Phoenix During Landing
05.26.08 -- A telescopic camera in orbit around Mars caught a view of NASA's Phoenix Mars Lander suspended from its parachute during the lander's successful arrival at Mars Sunday evening, May 25.

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494. IKE
5:38 PM CDT on May 27, 2008
Here's the GFS......

Link
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493. IKE
5:37 PM CDT on May 27, 2008
This system may park itself around the Yucatan for days according to the GFS latest run(18Z)...looks like it might eventually get drawn north or NE....
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491. juniormeteorologist
10:37 PM GMT on May 27, 2008
CAN I PLEASE HAVE THE GFS MODEL AND NOGAPS LINK????
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490. Michfan
5:28 PM CDT on May 27, 2008
That EPac TWD is very interesting indeed. Looks like these two seperate systems will converge later on. Will be interesting to see what NOGAPS has to say. Another thing i noticed on the GFS so far is the lack of rain in the SE US. That kinda sucks.
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489. Orcasystems
10:32 PM GMT on May 27, 2008
OMG, 90E
I logged on and saw that... figured the blog would be up in the thousands by now?
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488. TEXASYANKEE43
10:33 PM GMT on May 27, 2008
486

I ain't touchin that
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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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