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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238. Patrap
2:33 PM CDT on May 27, 2008

National Hurricane Preparedness Week
Link

History teaches that a lack of hurricane awareness and preparation are common threads among all major hurricane disasters. By knowing your vulnerability and what actions you should take, you can reduce the effects of a hurricane disaster. Hurricane Preparedness Week during 2008 will be held May 25th through May 31st.

The goal of this Hurricane Preparedness Web site is to inform the public about the hurricane hazards and provide knowledge which can be used to take ACTION. This information can be used to save lives at work, home, while on the road, or on the water.


Tuesday's Lesson.

High Winds

The intensity of a landfalling hurricane is expressed in terms of categories that relate wind speeds and potential damage. According to the Saffir-Simpson Hurricane Scale, a Category 1 hurricane has lighter winds compared to storms in higher categories. A Category 4 hurricane would have winds between 131 and 155 mph and, on the average, would usually be expected to cause 100 times the damage of the Category 1 storm. Depending on circumstances, less intense storms may still be strong enough to produce damage, particularly in areas that have not prepared in advance. Link
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237. weathersp
3:29 PM EDT on May 27, 2008
Its so wierd.. Ther are connected... but yet there are apart by land.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
236. smmcdavid
2:29 PM CDT on May 27, 2008
Hi gamma....

I tried to talk about the invest earlier, but no one seems interested. Strange I thought.
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235. tornadofan
7:29 PM GMT on May 27, 2008
Doc started the GW talk, not us. :)

I do tire of it though. 90E - where's it going? When does the Colorado State Site start doing it's models graph on it?
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234. Patrap
2:29 PM CDT on May 27, 2008


High Winds
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233. mixade
7:22 PM GMT on May 27, 2008
So what I'm getting out of this is that climate change is causing an increase in strong tornadoes but there's no evidence to back it up. I'm about the furthest thing from a conservative, but global warming alarmists are just so full of themselves it's unreal.

The planet is not dying. It's not sick, as Al Gore said, and it doesn't need to go to the doctor. Let's all just get a life.
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232. weathersp
3:16 PM EDT on May 27, 2008
Alpine lake is appxmatly 2 miles long by 1 mile across. Its spillway is 13.45 miles before dumping into the Missouri River. It crosses State Route 47 twice and State State Route 94 before dumping out near the town of Franklin,MO
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231. seflagamma
3:28 PM AST on May 27, 2008
yes!!!!! no more GW or CC discussions we have a real invest to talk about now!
Member Since: August 29, 2005 Posts: 299 Comments: 40915
229. seflagamma
3:23 PM AST on May 27, 2008
222. cdo 3:22 PM AST on May 27, 2008
My prediction, first storm will form on July 4, 2008


no no no no no....we are all wishcasters here, and for the past few years we are use to having our named storm in May or June..we had TS Barry on June 1st last year. July is way to far for a named storm... perhaps our first hurricane, but not our first storm of the year... the Atlantic basin is a big territory and lots of room for a named storm to be formed before July 4th.

(do not be offended, just being funny not picking on you)

Gams
Member Since: August 29, 2005 Posts: 299 Comments: 40915
228. Drakoen
7:25 PM GMT on May 27, 2008
224. smmcdavid 7:23 PM GMT on May 27, 2008
Hi Drak... hope you are ready for this today. Take a few minutes to prepare if needed. lol


lol i'm ready. I need to look over the models and the satellite loops to get caught up with everything.
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227. Patrap
2:24 PM CDT on May 27, 2008

225. afcjags03

profound...thanks
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226. cdo
7:23 PM GMT on May 27, 2008
it will be interesting to see if the Cape Verde season starts earlier than normal, that area seems to be the only area with more than slightly above average SSTs
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225. afcjags03
7:20 PM GMT on May 27, 2008
Boy if I had a dollar for every time I saw or heard, "but we don't yet know enough", or, "more research needs to be done.", i'd be rich!

Yet, people still believe what they choose to believe. Talk about cyclical.

GW is getting very old, wish everyone would just shut up for a good quarter century and then try to come back and validate or be proven wrong on their beliefs and what they know as "fact."

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224. smmcdavid
2:23 PM CDT on May 27, 2008
Hi Drak... hope you are ready for this today. Take a few minutes to prepare if needed. lol
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223. Drakoen
7:21 PM GMT on May 27, 2008
Good afternoon everyone.
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222. cdo
7:20 PM GMT on May 27, 2008
My prediction, first storm will form on July 4, 2008
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221. hurricane23
3:18 PM EDT on May 27, 2008
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220. kmanislander
7:16 PM GMT on May 27, 2008
With 90E getting its act together the odds of a SW Caribbean system have now diminished in the short term.

90E would have to move away from the area and shear would need to slacken for anything to organise N of Panama IMO. The available energy is now being largely drawn into the EPAC
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219. Patrap
2:19 PM CDT on May 27, 2008
Funnel Cloud Photos from a few Hours ago,St. LouisLink
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218. Inyo
7:10 PM GMT on May 27, 2008
GulfScotsman, dinosaur farts release methane, not CO2. They didn't realy affect the co2 cycle. That being said, the perceived difference between the dinos and us is that we should be able to see the long-term consequences of our actions and divert them before they kill us off. However, that may be too optimistic, and we may be a species that has evolved enough intelligence to recognize that our actions may greatly decrease our chance of survival, but with too much of the competitive and hoarding instincts built in to actually reverse the process. This would mean in effect we are just smart enough to know how much #%$# we have gotten ourselves in.

And yeah, the earth will be fine. It may get a bit swampy for a while... not too good for humans, and most of us will probably die off. But the swamps and rain forests will have the last laugh, and will end up covering our ruins and go back to fixing carbon like they did before we got here.

Or maybe we'll actually fix the problem. Anything is possible I suppose.
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217. smmcdavid
2:15 PM CDT on May 27, 2008
Now that we have an invest... when/if will it become a depression? Any guesses?
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215. KrazyKaneLove
7:11 PM GMT on May 27, 2008
ty Patrap, I'm off to work everyone, Stay COOL...
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214. NEwxguy
7:12 PM GMT on May 27, 2008
See my invest dance worked.now we can return to our original programming
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213. cchsweatherman
3:12 PM EDT on May 27, 2008
Soon I'm expecting a Special Tropical Disturbance Statement from the NHC for the Eastern Pacific. By the way, under what criteria does the NHC issue a Special Tropical Disturbance Statement?
Member Since: April 14, 2007 Posts: 8 Comments: 5169
212. StormHype
7:08 PM GMT on May 27, 2008
What's up with those annoying fish-eye lens storm pics? Someone get a new toy and not figure out how to correct the lens distortion in PS yet?
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211. hurricane23
3:13 PM EDT on May 27, 2008
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210. Weather456
3:06 PM AST on May 27, 2008
TRMM capture the system...nothing really impressive at the surface as yet. 25 knots; 1007 mb.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
209. Patrap
2:11 PM CDT on May 27, 2008

Warren County Officials Check for Seepage in Dam
Created: 5/27/2008 1:22:03 PM
Last updated: 5/27/2008 1:39:02 PM KSDK News Link
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208. cdo
7:04 PM GMT on May 27, 2008
looks like we had a "ghost" teaser storm Aruthor....will be a few weeks (probably mid July) before we get him.
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207. kmanislander
7:03 PM GMT on May 27, 2008
90E is entirely consistent with the set up we were discussing this morning as well as climatology. No surprises there.
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206. seflagamma
3:04 PM AST on May 27, 2008
yes, all climate change discussions need to be on the proper blog for that topic; it is too much of a heated topic to just do a few posts here and not expect a passionate rebutal from someone.

This is now officially a tornado or tropical weather blog!
Member Since: August 29, 2005 Posts: 299 Comments: 40915
205. cchsweatherman
3:04 PM EDT on May 27, 2008
Just stopping back in to let everyone know that the NAVY site now has Invest 90E in the Eastern Pacific from the broad low we have been watching for the past 24 to 36 hours.
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204. seflagamma
3:03 PM AST on May 27, 2008
oh I see now Invest 90 in Pac, but one of the models has it going into Gulf so that may need watching...
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203. Greyelf
2:03 PM CDT on May 27, 2008
As OSUWXGUY said earlier: "Trying to refute others or prove your beliefs on this blog is not very productive - there is a climate change section now - go there."

Guess what GW debaters - there really IS a climate change blog. It's not fantasy. Here it is! Link

Use it. Please.
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202. AWeatherLover
6:58 PM GMT on May 27, 2008
Is everyone discounting the models now? Are they having a hard time adjusting to the season beginning or something?
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201. KrazyKaneLove
7:01 PM GMT on May 27, 2008
Patrap , this is in St. Louis?
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200. seflagamma
3:00 PM AST on May 27, 2008
pat, whooo that sounds serious for south of the St Louis area. I know that area has had some flooding lately.

cch,
so it is an offical invest??? but I don't count the ones in the Pacific...only the ones in the Atlantic basin (or Carribean or Gulf, etc) you know the ones that affect most of us here... sort of selfish that way you know (just kidding)
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199. Patrap
2:00 PM CDT on May 27, 2008
We know, but TYVM.


151. nash28 1:38 PM CDT on May 27, 2008
Invest 90 is now up for the EPAC.
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198. Patrap
1:59 PM CDT on May 27, 2008
NEXRAD Radar
St. Louis Base Reflectivity 0.50 Degree Elevation Range 124 NMI Link
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197. cchsweatherman
2:57 PM EDT on May 27, 2008
Just stopping back in to let everyone know that the NAVY site now has Invest 90E in the Eastern Pacific from the broad low we have been watching for the past 24 to 36 hours.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
196. seflagamma
2:58 PM AST on May 27, 2008
Thank you all for your support! LOL
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195. Patrap
1:57 PM CDT on May 27, 2008
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
104 PM CDT TUE MAY 27 2008

...ALPINE DAM IN INNSBROOK LEAKING AND COULD POSSIBLY FAIL...

AT 1230 PM THE WARREN COUNTY EMERGENCY MANAGEMENT AGENCY
REPORTED THAT THE ALPINE DAM WITHIN THE INNSBROOK ESTATES AREA
WAS LEAKING AND COULD POSSIBLY FAIL.

THE ALPINE DAM IS AN EARTHEN DAM LOCATED ON THE SOUTH END OF
ALPINE LAKE AND IS SPANNED BY ALPINE LAKE DRIVE. IF THE DAM
FAILS...THE WATER WOULD FLOW SOUTH AND INTO CHARRETTE CREEK AND
ACROSS CHARRETTE CREEK ROAD. ALL PERSONS IMMEDIATELY DOWNSTREAM OF
THE ALPINE DAM SHOULD BE PREPARED TO MOVE TO HIGH GROUND
IMMEDIATELY.
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194. NEwxguy
6:56 PM GMT on May 27, 2008
lol,ok gamma no sports,hears a revelation,lets talk tropics...............dead silence
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193. seflagamma
2:56 PM AST on May 27, 2008
last time I checked, didn't we have some models trying to develope a system for us??? something exciting for later inthe week????

why aren't we busy wishcasting that possible invest???? (or did I already miss that part of the conversation?)
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192. KrazyKaneLove
6:55 PM GMT on May 27, 2008
lol NE..
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190. weathersp
2:56 PM EDT on May 27, 2008
Member Since: January 14, 2007 Posts: 17 Comments: 4140
189. seflagamma
2:55 PM AST on May 27, 2008
NOOOOO no sports in here or I will have to talk about the Cardinals for baseball and the Dolphins for Foot ball and Jason Taylor comingin 2nd place on Dancing with the Stars!
Member Since: August 29, 2005 Posts: 299 Comments: 40915
188. weathersp
2:54 PM EDT on May 27, 2008
Increaseing Vorticity in th EPAC.. not much in the SCAB.
Member Since: January 14, 2007 Posts: 17 Comments: 4140

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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.