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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Where does the 11 million lbs of Daily Pollutants from combustion of Fossil Fuel Emission's go ?
To Boca,but of course.
If it's so clear, then print the evidence that makes this fact.
I've heard the phrase and I agree with it at times, "It takes more FAITH to believe in science than it does religion."
How bout dat drought though?
People are entitled to have doubts about whether WE cause climate change or not.
The very hard truth, is that climate change is ONE of the potential results of our actions. Hard to prove, easy to diss.
The easy ones to prove are
loss of habitat
deforestation
destruction of Nature as we know it.
The list can go on for pages, but none of the items on the list directly affect our bank account. Yet.
So we can all rest assured, that everything is hunky dory............
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. SIMILAR PRECIPITATION IS WEST OF THE CENTER
WITHIN 30 NM ON EITHER SIDE OF LINE FROM PANAMA NEAR 9N81W
TO 11N82W. THE 57W/58W TROPICAL WAVE MAY REACH THE EASTERN
CARIBBEAN SEA DURING THE NEXT 24 HOURS OR SO BASED ON ITS
CURRENT MOVEMENT OF 15 TO 20 KT. SHOWERS AND THUNDERSTORMS
ACCOMPANY THIS WAVE.
So, I was incorrect in saying there was a surface low.
Okay, back to the tropics. No hard feelings jp, just different opinions.
Or that 4000 square Mile Dead Zone off the La.Coast in the GOM caused by the Miss River Nitrogen runoff from idiotic Farm Practices Upriver in the Farm Belt.
Naw...it not a worry, unless you Like Shellfish or Have Gills.
Global Climate Change Black De-Forested Cake with Chad icing..
Ummmmmmmmmmmmmmmmmmmmmmmmmmmmmm...good.
That's the dumbest statement I've ever seen Dr. Masters write.
Not necesarily incorrect...typical surface reflection is seen west of mid-upper level circulations...that is what was being picked up by the surface observations.
Lurkers swarm to the Prey like Amazon Piranha's to a Crossing Cow..
And I thought it was a work of literary Genius, ( how do you spell that ). Shear poetry, with pathos, drama, suspense.
Oh well. I'll go back to being mundane.
heheheh
A hurricane's "hot towers" can increase its intensity by adding power to boost the storm's heat engine. For the first time, research meteorologists have run complex simulations of these phenomena using a very fine temporal resolution. They have combined this new simulation data with satellite observations to study the innerworking of the "hot towers" in never-before-seen detail. Link
The Earth will still be here folks, just like it was before we were here. We are a tick, a flea if you will on the Earth's back. She can shake us off in a blink.
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