The tornado season of 2008: climate change to blame?

[phantom power]

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.

[RL3AO]

1. Correct. These are not hurricanes.

A degree or two of warming can have a drastic effect on hurricanes, they won't on tornadoes. This season has been active because the weather pattern has been active.

[NCDem60]

2. You have to be careful not to

read to much into Atlantic hurricanes. For instance, the two years this decade when there were much above normal Atlantic seasons, in the Pacific they had a lower than average number of typhoons. The function of tropical systems is to move hot air away from the tropics thereby keeping the system in balance. As the prevailing winds circle the earth it really doesn't matter where the storms occur as far as moving the hot air north is concerned.

[RL3AO]

3. I'm a weather geek and tropical cyclones are my drug of choice.

The WPac has been slightly below average and the EPac has been normal. The Atlantic is in an active phase because of the AMO. Personally, I think human caused GW is way overblown, but I don't bring it up here often because I don't care to argue against everyone.

[phantom power]

4. Oops, forgot to cite the link:

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=948&tstamp=200805

[Shoelace]

5. NASA study ('07) points to connection with GW/extreme weather, more tornadoes

Global Warming Will Bring Violent Storms And Tornadoes, NASA Predicts
ScienceDaily (Aug. 31, 2007) —

NASA scientists have developed a new climate model that indicates that the most violent severe storms and tornadoes may become more common as Earth's climate warms.


Previous climate model studies have shown that heavy rainstorms will be more common in a warmer climate, but few global models have attempted to simulate the strength of updrafts in these storms. The model developed at NASA's Goddard Institute for Space Studies by researchers Tony Del Genio, Mao-Sung Yao, and Jeff Jonas is the first to successfully simulate the observed difference in strength between land and ocean storms and is the first to estimate how the strength will change in a warming climate, including "severe thunderstorms" that also occur with significant wind shear and produce damaging winds at the ground.

>>>

The central and eastern areas of the United States are especially prone to severe storms and thunderstorms that arise when strong updrafts combine with horizontal winds that become stronger at higher altitudes. This combination produces damaging horizontal and vertical winds and is a major source of weather-related casualties. In the warmer climate simulation there is a small class of the most extreme storms with both strong updrafts and strong horizontal winds at higher levels that occur more often, and thus the model suggests that the most violent severe storms and tornadoes may become more common with warming.

The prediction of stronger continental storms and more lightning in a warmer climate is a natural consequence of the tendency of land surfaces to warm more than oceans and for the freezing level to rise with warming to an altitude where lightning-producing updrafts are stronger. These features of global warming are common to all models, but this is the first climate model to explore the ramifications of the warming for thunderstorms.

http://www.sciencedaily.com/releases/2007/08/070830105911.htm


note: one thing that I wonder is this; the lower, mid troposphere is warming while the stratosphere is cooling (this was predicted in early climate models)
so would this not add to the strength of these systems given the temps difference alone - more turbulence, etc.?

Also, 2008 is on track to break all records if trends continue for number and strength of tornadoes. The number of fatalities has already broken previous records (just heard that last night on the Weather channel) even with far better warning systems in place. See details here:

http://www.spc.noaa.gov/climo/torn/monthlytornstats.html

[FREEWILL56]

6. "Doppler radar can only "see" perhaps 50% of all tornadoes,

and many of those it detects never touch down."

Any funnel that does not touch the ground is not a tornado. I found this out the hard way as I had reported a funnel to the National Weather Service and they said they will not issue a tornado warning unless it has touched the ground. As per their definition of a tornado is a funnel that reaches touch down and is confirmed by site or other evidence after the fact of a touch down. Prior to that is only a tornado watch, but this does not indicate whether any funnels are out there or not, even if some are seen and reported. The NWS needs an interim catagory to indicate these funnels when sited as the danger of a tornado is heightened when funnels are sited.
That does reinforce the fact that if we could accurately count the tornados, which we can't, then there would not be anything accurate to compare those figures to from the past to say one way or the other of any trends because we couldn't accurately count them then.