The tornado season of 2008: climate change to blame? And, tropical update
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
Missing House, if found call Dennis and Carla
Nice structure on upercell east of Pratt, Kansas. Photo copyright Mike Theiss.
Reader Comments
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RAMSDIS GOES-12 4km VISIBLE LOOP
Gee,..a Oil futures Guy.
Arent you the Guy who posted about your buisness the other day?
Interesting stuff from the EPAC TWD...
Yes, very interesting...
chilling out?
what is it having a smoke or a cocktail? LMAO
EPAC has 90E, what is being said about that?
lol. I tried to be funny...
The total damage from Katrina is estimated at $81.2 billion (2005 U.S. dollars), nearly double the cost of the previously most expensive storm,
Betsy in 65 was the First Billon Dollar Baby..
Yellow areas have the potential for dust, but blowing dust is generally noted by orange and red colors.
It may be clear to him ....but there are many learned scholars that are equally sure that his statement is not correct and not proven.
From how I interpret the GFS is that 90E moves close to Central America then a low develops in the SW Caribbean and absorbs 90E.
You got it.
SEE HERE and HERE
One thing to keep in mind is once high pressure builds more in the upper layers unfavorable conditions may relax a bit.
I give both the EPAC and the Caribbean area the same chance for development. If anything I would favor the EPAC a little bit more because of climatology
I agree
468.
Certainly...
Take the opportunity now to Store Fuel for a Possible Evactuation,add some stable mix, and store Properly.
One will be one step ahead of the fray. If a threat develops and one has to bug out.
According to the last few runs of the GFS...this disturbed weather(around central America), is going to move WNW over the next 5 days.....
WNW then NNW into the Gulf of Honduras.
On a practical note I have a modest place in the keys which I avoid staying in during the Hurricane season, the reason is that I can't stand the evacuations which we have seen in recent years. I am paying a crazy 5 figure sum for insurance on this property and I feel less and less safe living in it, I will look at selling up some day. For now, I am lucky enough to have another property in Florida. This one is concrete built with steel window shutters and I will feel confident inside in a cat 1 or 2. Theoretically it would stand a cat 4 but I wouldn't be there to find out. Andrew was enough to teach me to flee a big storm. I don't know too many people that have been thru a cat 4/cat 5 that would repeat the experience
Will the BOC have favorable conditions by Mon.?
Thanks, that answers my ? for 481.
On another note, our local met in Houston has retired. Does anyone remember Dr. Neal Frank?
Looking forward to your daily synopsis reports.
I ain't touchin that
I logged on and saw that... figured the blog would be up in the thousands by now?
Link
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.
Link
just a wave maker and bringer of rain to SWFL.
Kitchen is calling BBL
http://www.bvipirate.com/NOGAPS.phtml
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