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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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
187. NEwxguy
6:53 PM GMT on May 27, 2008
Krazy,can we keep the discussion on the Chiefs?
Member Since: September 6, 2007 Posts: 878 Comments: 15739
185. KrazyKaneLove
6:47 PM GMT on May 27, 2008
I had 3rd row seats on the visitors 20 yd line..it did rain a little , but it was nice to see right before Depressing Wilma..my mom was visiting from KC and was psyched cuz its so hard to get tickets at Arrowhead.. also I got to see Priest Holmes play..hadn't realized how fast he was from the t.v. Hopefully we have a better than average season:)Back to the GW debate...boring..
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184. NEwxguy
6:52 PM GMT on May 27, 2008
Winds of Change!!!!!
Member Since: September 6, 2007 Posts: 878 Comments: 15739
183. seflagamma
2:48 PM AST on May 27, 2008
#175, GulfSM, you amaze me sometimes! loved that post and I don't always agree with you!
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182. Patrap
1:45 PM CDT on May 27, 2008
As the Aliens explained to Me in Tromso in "84".

"Patrap...until the driving force of the Planet changes from the Gathering of Wealth and Murder.
We Will be watching..and ready to take action when deemed necessary"

The Antarians make an excellent Chowda too.
Member Since: July 3, 2005 Posts: 424 Comments: 128284
181. NEwxguy
6:47 PM GMT on May 27, 2008
don't touch that dial, we will return to our normal tropical weather programming after a brief 4 hr GW discussion
Member Since: September 6, 2007 Posts: 878 Comments: 15739
180. smmcdavid
1:47 PM CDT on May 27, 2008
LOL press... funny stuff.
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179. presslord
2:45 PM EDT on May 27, 2008
Hey!! I just got done with a heavy GW discussion.....What's going on with the storm?????
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178. Bamatracker
6:44 PM GMT on May 27, 2008
yes krazykane....i am a fanatical chiefs fan. My dad and bro live up there and have season tickets. I get the sunday ticket so i dont miss a game. that wilma game ticked me off because it didn't get aired by directv. I listened to it on the radio and watched the gameday on espn's site.
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177. NEwxguy
6:46 PM GMT on May 27, 2008
Your right Pat,one should never look back
Member Since: September 6, 2007 Posts: 878 Comments: 15739
176. OSUWXGUY
6:41 PM GMT on May 27, 2008
Does anyone out there have a tropical Atlantic ITCZ climatology graphic. I have seen one for Africa, but not over the MDR.
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173. Patrap
1:42 PM CDT on May 27, 2008
Most never Look back in the blog when entering.

Like,"Hey man, I just came from Jiffy Lube,got my Oil Changed in My SUV".

"Whats Happening with the Storm"?

Member Since: July 3, 2005 Posts: 424 Comments: 128284
172. KrazyKaneLove
6:38 PM GMT on May 27, 2008
Bama, are you a chiefs fan? I saw your pic of Arrowhead. My family is from K.C.umm, to keep this weather related, I saw them beat Miami at Proplayer right before Wilma came in..it was the game they had to adjust due to the storm.
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171. kmanislander
6:41 PM GMT on May 27, 2008
From the TWD . This underscores why, as I posted earlier, one should not rely entirely on a sat image in order to decide whether a surface low exists or not. The feature in the S Caribbean is in the mid to upper levels at this time.

"Scattered strong showers and thunderstorms are from 10n to 13n
between 75w and 80w...to the east of a middle to upper level
cyclonic circulation center in the southwestern corner of the
area near 11n81w "
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170. TexasRiverRat
6:41 PM GMT on May 27, 2008
Who has declared this an invest 90? It hasnt showed up on the Navy site???
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169. pottery
2:41 PM AST on May 27, 2008
Scott. You are correct.
I get het-up !
Peace and nuff respect...........
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167. presslord
2:40 PM EDT on May 27, 2008
jp...look...I swear I'm not trying to argue...but I can find just as much evidence that we aren't going into recession as you can find evidence that humans don't contribute to GW...

the fact is this: respectful debate is a healthy part of the scientific process...
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166. NEwxguy
6:40 PM GMT on May 27, 2008
158. JFV 6:39 PM GMT on May 27, 2008
Really, how come NE!

Look back at the past entries,the discussion is global warming,nothing as mundane as Tropical systems and possible invests
Member Since: September 6, 2007 Posts: 878 Comments: 15739
164. CaneAddict
6:38 PM GMT on May 27, 2008
151. nash28 6:38 PM GMT on May 27, 2008
Invest 90 is now up for the EPAC.
Action: | Ignore User


I would think soon they will declared Invest 90L also...
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163. Patrap
1:40 PM CDT on May 27, 2008
A Tropical Recession..I gotta look that one up..BRB>
Member Since: July 3, 2005 Posts: 424 Comments: 128284
162. OSUWXGUY
6:29 PM GMT on May 27, 2008
Good Afternoon Everyone!

It's sad how vitriolic this debate has gotten, and based on the passion on each side it's obviously important to many people.

Everyone on this blog is interested in weather, right?

Take the time to do your own reading on the research being done, and think for yourself when it comes to climate change.

Trying to refute others or prove your beliefs on this blog is not very productive - there is a climate change section now - go there.
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161. scottsvb
6:36 PM GMT on May 27, 2008
pottery...I'm not going into the GW issue with you.. its pointless for anyone to argue 1 side vs another.

Mich.. you can see on the visible the LLF of the vortex but you cant on infr...opposite goes with the midlevel.. you can see it on inf...
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160. nash28
2:39 PM EDT on May 27, 2008
Bama- Just go to the Tropical Page here.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
157. Bamatracker
6:39 PM GMT on May 27, 2008
can i get that link nash?
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156. Patrap
1:38 PM CDT on May 27, 2008
There goes the Invest...west.
Member Since: July 3, 2005 Posts: 424 Comments: 128284
153. presslord
2:35 PM EDT on May 27, 2008
ah....actually..we are not in a recession....
as we were discussing the sins voicing opinions without evidence, it seems appropriate to point that out....
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152. Patrap
1:38 PM CDT on May 27, 2008
Anytime..LOL
Member Since: July 3, 2005 Posts: 424 Comments: 128284
151. nash28
2:38 PM EDT on May 27, 2008
Invest 90 is now up for the EPAC.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
150. CaneAddict
6:37 PM GMT on May 27, 2008
Thought it was interesting that Accuweather.com has tooking a good deal of interest into the disturbed area in the southern Caribbean...along with 2 of their top bloggers interested in it....
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149. Littleninjagrl
6:36 PM GMT on May 27, 2008
Thanks Bama.
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147. Patrap
1:35 PM CDT on May 27, 2008
well the sad thing is that there is so much more to worry about then this BS that will likely not manifest itself into anything significant for hundreds of years at least

I feel the same about that Caribbean System too Jp
Member Since: July 3, 2005 Posts: 424 Comments: 128284
146. pottery
2:29 PM AST on May 27, 2008
post 124 scott.
Why do you feel so impotent, that you are unable to change things.?
Try and detirmine for yourself, whether there is anything that YOU can do, or stop doing, to make an impact on what you call "the earths cycle"
Plant a tree.
Or go out and cut one down.
All actions have re-actions.
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145. tornadofan
6:30 PM GMT on May 27, 2008
Where in all those pretty charts does it show MAN causing that warming (or WOMAN for that matter)?
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144. Michfan
1:33 PM CDT on May 27, 2008
scott got a ? for you. In the last blog you mentioned mid level vortexes. What is the best way to determine whether a circulation is mid level surface reflection or an actual closed low on visible sat imagery?
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143. Bamatracker
6:34 PM GMT on May 27, 2008
NWS tampa

WE CONTINUE TO WATCH THE
EVOLUTION OF A LARGE BUT BROAD AREA OF LOW PRESSURE NEAR CENTRAL
AMERICA. AS IT STANDS NOW...THE CIRCULATION APPEARS TO BE MOSTLY IN
THE EASTERN PACIFIC...WHICH IS WHERE THE INITIAL DEVELOPMENT TAKES
PLACE IN THE VARIOUS MODEL SUITES. AT THIS TIME...THERE IS NO WAY TO
DETERMINE WHAT EFFECTS...IF ANY AT ALL...WE WOULD SEE FROM THIS
SYSTEM IN THE EXTENDED PERIOD. THE LATEST GFS RUN KEEPS THE
CIRCULATION WELL TO THE SOUTH AND MAINLY OVER LAND THROUGH AT LEAST
TUESDAY. THIS IS SIMILAR TO THE 00Z ECMWF RUN...BUT RUN TO RUN
CONSISTENCY AMONG INDIVIDUAL MODELS IS TERRIBLE. WITH SUPPORT FROM
BOTH THE 00Z ECMWF AND THE 12Z GFS...I WILL CONTINUE TO KEEP IMPACTS
FROM THIS SYSTEM OUT OF THE FORECAST.
Member Since: Posts: Comments:
140. DocBen
6:31 PM GMT on May 27, 2008
Thanks for the graphs MichaelSTL. The deniers don't seem to want to see reality.

Back to the Carib - is that blob getting organized? Especially; any southward wind on its west side to separate it from the EPAC?
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139. scottsvb
6:32 PM GMT on May 27, 2008
latin that is from a dying cold front (shortwave)
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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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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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