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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988. Weather456
11:57 PM AST on May 27, 2008
984. JFV 11:55 PM AST on May 27, 2008
WOW, Weather did that discussion just absically confirmed that a tropical cyclone will indeed form in the carib within the next few days? If I just read it correctly that is!


Not predicting a tropical cyclone on the Caribbean but rather the surface low being forecast by models (TD status likely). Also any development will be slow to occur until the upper anticyclone forms and not much will develop before it begins to interact with central america. But there are now two surface lows in either basin with 90E the more organize and more likely to develop.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
987. KEEPEROFTHEGATE (Mod)
11:58 PM EDT on May 27, 2008
jfv withn or just after 27 hrs from now
3 am may 29 2008 imo
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985. Weather456
11:51 PM AST on May 27, 2008
As recommended, the NHC added a new wave to their surface maps
Member Since: July 24, 2005 Posts: 407 Comments: 19076
983. Beachfoxx
10:47 PM CDT on May 27, 2008
Evening everyone...

just stopping by to see what's twirling out there. The local WX hyped it up big time! LOL
Guess they want everyone to "stay tuned"...

Right now that blob is just a blob,
but to hear those guys. Whew, better pack the bags and be ready to go!
Member Since: July 10, 2005 Posts: 157 Comments: 29383
982. Weather456
11:12 PM AST on May 27, 2008
Surface Low in the Caribbean




A BROAD AREA OF SURFACE LOW PRESSURE DOMINATES THE SW CARIBBEAN
AND THE E PAC ALONG THE COAST OF CENTRAL AMERICA. ALTHOUGH
SEVERAL CYCLONIC SWIRLS ARE NOTED WITHIN THIS AREA...THE OVERALL
PATTERN SEEMS TO SUGGEST SLIGHT ORGANIZATION CENTERED ON ROUGHLY
09N89W. THIS IS WHERE OUR MARINE PRODUCTS HAVE SUGGESTED A
SURFACE LOW...POSSIBLY A TROPICAL CYCLONE...WOULD DEVELOP. MODEL
GUIDANCE CONTINUES TO SUGGEST THAT THIS LOW PRESSURE WILL
MEANDER IN THIS AREA FOR THE NEXT DAY OR SO...AND PERHAPS DRIFT
NE LATER THIS WEEK. THE UPPER PATTERN IS ALSO NOT EXPECTED TO
CHANGE TONIGHT AND EARLY WED BUT THEREAFTER SEVERAL CHANGES ARE
FORECAST. AN UPPER LOW WILL SPIN UP OVER THE BAY OF CAMPECHE...
OR CUT OFF FROM AN UPPER TROUGH...AND DRIFT S FRI WHILE AN UPPER
ANTICYCLONE DEVELOPS OVER THE SW CARIBBEAN REPLACING THE UPPER
TROUGH CURRENTLY DISSECTING THE CARIBBEAN. THIS WOULD ALLOW A
SURFACE LOW TO MOVE NW ACROSS CENTRAL AMERICA OVER GULF OF
HONDURAS. SHOULD ALSO MENTION THAT GUIDANCE SUGGESTS A SECOND
LOW PRESSURE WILL DEVELOP OVER THE SW CARIBBEAN AND MOVE NW
THROUGH 72 HOURS. THE APPROACHING TROPICAL WAVE MENTIONED ABOVE
MAY ADD THE NEEDED LOW LEVEL VORTICITY TO GET ALL OF THIS
SPINNING.
NOTE THAT THE GRADIENT S OF THE E PAC LOW PRESSURE IS
ALREADY SUPPORTING A SW TO W 20 TO 25 KT WIND AND SEAS TO ABOUT
11 FT. THESE CONDITIONS ARE EXPECTED TO PERSIST S OF THE LOW
THROUGH 48 HOURS.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
981. sporteguy03
3:45 AM GMT on May 28, 2008
Deep Convection with 90E seems to be getting better organized
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979. presslord
3:41 AM GMT on May 28, 2008
tampa...that's pretty impressive....
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978. TampaSpin
11:39 PM EDT on May 27, 2008
I guess i have caused enough trouble for the night, its been a long day. Good night all.
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977. ATS3
3:32 AM GMT on May 28, 2008
GOOD EVE
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976. smmcdavid
10:34 PM CDT on May 27, 2008
Hi all.... what have I missed?

Looks like the gangs all here.
Member Since: September 20, 2005 Posts: 31 Comments: 2309
975. TampaSpin
11:28 PM EDT on May 27, 2008
GFDL at 126hours...in the BOC
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974. pottery
11:17 PM AST on May 27, 2008
Greetings. Just back from an adventure with Indiana Jones.
What happened to all the rain that was lurking just east of me this afternoon ?? Looks to have gone astray..........
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973. moonlightcowboy
10:15 PM CDT on May 27, 2008
Ugh, Press - but I salute his aspirations!
Member Since: July 9, 2006 Posts: 184 Comments: 29594
972. TampaSpin
11:13 PM EDT on May 27, 2008
970. vortfix 11:12 PM EDT on May 27, 2008
Oh.....oh.....Please ask for more pity!


Vortfix you do have my pity


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971. presslord
3:09 AM GMT on May 28, 2008
another thing y'all should know...my son started taking flying lessons at 14....six months ago (on his 16th birthday) he soloed...he's a regular WU junkie and lurker here....and thanks largely to you folks he wants to fly hurricane hunters...his mother is really pissed about it...but I'm kinda proud...
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970. vortfix
3:12 AM GMT on May 28, 2008
Oh.....oh.....Please ask for more pity!
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967. taco2me61
3:06 AM GMT on May 28, 2008
Press,
I had no idea that you have been on here that long.... come to think of it I might have been here for over 5 years now..... Heck just can't remember..... But anyway i try to be careful on what i say in here because some do blast me if I'm wrong.... So I just sit back and read, then say very little if you know what i mean....


Taco :0)
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966. TampaSpin
11:08 PM EDT on May 27, 2008
Jp your after rains should be coming soon in the Orlando area.....lol
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965. mgreen91
3:08 AM GMT on May 28, 2008
Unmanned Drones Head into Hurricanes' Core to Get Data


Government scientists believe a fleet of small unmanned airplanes sent to hurricanes' cores could lead to revolutionary advances in storm forecasting and measurement.


The drones are able to fly far lower than manned hurricane hunter planes and can beam back information from close to the ocean's surface, where conditions fuel a storm's intensity.

The National Oceanic and Atmospheric Administration began launching drones in 2005, and they've proved so durable and effective that they've been called pioneering.

"It's going to be a revolution in earth system monitoring,'' said Marty Ralph, who heads NOAA's unmanned aircraft efforts. "Like the development of satellites in the 60s and 70s and of weather radar in the 30s and 40s, both of which are fundamental elements of our weather measurement and prediction, it's in the same class.''

Until now, scientists relied solely on hurricane hunters that typically fly at 10,000 feet, though sometimes as low as 5,000 feet, and drop measuring instruments to the ocean. The instruments transmit somewhat random data from points on their way from the plane to the sea, but are unable to provide consistent readings from points close to the water's surface.

The drones fly as low as 300 feet and can go more than 2,000 miles without refueling. The probes on board are not as high-frequency as those on manned flights, but because of their consistent readings from a low altitude, they've been able to give scientists valuable data they've never before been able to gather.

Measures of pressure, temperature, winds and humidity can be beamed back to the National Hurricane Center frequently to help meteorologists better determine a storm's strength.

"This will give the hurricane center what it wants most,'' said Joseph Cione, a lead scientist on NOAA's drone project. "And it will help researchers understand better the interaction between the ocean and the atmosphere.''

Scientists don't envision the drones will replace manned flights. They say they can work in tandem to help plot the most crucial spots in a storm. Within a few years, Ralph said, he expects drones to be dispatched in every storm, a move scientists hope will vastly improve the understanding of how the ocean's temperature intensifies and weakens storms.

"My job ultimately is to save lives and reduce damage of property,'' Cione said.

NOAA is currently using Australian-made Aerosonde Mark 3 planes weighing about 28 pounds and with a 9-foot wingspan. The 1.6-horsepower engine propels it forward at 60 mph, but it benefits from strong tail winds. In Hurricane Ophelia in September 2005, it reached speeds of 150 mph.

The drone has no wheels. It takes off atop an SUV that releases the plane when it reaches about 50 mph. It lands on its belly, preferably on a grassy area.

In test missions in Hurricane Noel last year and during Ophelia, the Aerosonde came back in good condition. Scientists concede they'll eventually lose one of the roughly $50,000 planes, but it may be a conscious choice to keep it out longer to gather crucial data to save lives.

"We don't really want to be burning up aircraft,'' Cione said, "but sometimes that makes sense.''

The drones are also being used beyond the realm of tropical storms. NOAA has completed or planned drone missions examine low-level jet streams that affect West Coast weather; to gather data about pollution over the Indian Ocean; to study the rapid melting of ice on the North Slope of Alaska and its effect on seals there; to monitor whale migration; and to mitigate illegal fishing in the Northwestern Hawaiian Islands.

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963. moonlightcowboy
9:59 PM CDT on May 27, 2008
Another thing, too, as the MJO cycles back around in mid July(+,-), as the CV season approaches, it could be more significant if ENSO conditions continue to move more towards neutral.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
962. Swells22
3:00 AM GMT on May 28, 2008
Thank you very much KmanIslander at 938. I remember you from last season. StormW seemed very helpful too... sam
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961. presslord
3:03 AM GMT on May 28, 2008
BTW taco...you're right...there is no better learning environment on the web than this blog....
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960. presslord
3:01 AM GMT on May 28, 2008
thanks taco...I've been around here 3 years...most of these folks know by now that I have a slightly twisted sense of humor....thanks for the kind words...
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959. Michfan
10:02 PM CDT on May 27, 2008
90E needs some love i tell ya.
Member Since: September 7, 2007 Posts: 0 Comments: 1666
958. Drakoen
3:00 AM GMT on May 28, 2008
oh btw the EPAC low is down to 1004mb and the SW Caribbean system now has an area of low pressure at 1006mb. Will be interesting to see what happens tomorrow.
Member Since: October 28, 2006 Posts: 57 Comments: 29919
957. presslord
3:00 AM GMT on May 28, 2008
they seem to be mlc...Any potential of anything coming of it in the near future?
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955. taco2me61
2:56 AM GMT on May 28, 2008
Press,
You can ask away.... There are some in here that can answer anything you ask..... If there is anything you want to know about the weather.... They are in here....

Myself I have been on this blog for over 4 years now and have learned alot, but I do lurk on here......

Again welcome to Weatherunderground we are glade you came....

Taco :0)
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954. Drakoen
3:00 AM GMT on May 28, 2008
952. moonlightcowboy 2:58 AM GMT on May 28, 2008
Have a good sleep, K'man, cchs and whomever headed that way.


I'm headed that way. Good Night!
Member Since: October 28, 2006 Posts: 57 Comments: 29919
953. kmanislander
2:59 AM GMT on May 28, 2008
So long MLC

Busy times are coming LOL
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952. moonlightcowboy
9:58 PM CDT on May 27, 2008
Have a good sleep, K'man, cchs and whomever headed that way.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
951. cchsweatherman
2:57 AM GMT on May 28, 2008
Good night all. Will be back tomorrow AM.
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950. kmanislander
2:56 AM GMT on May 28, 2008
well I am out for tonight

Will chat tomorrow. Have a great one all
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949. TampaSpin
10:55 PM EDT on May 27, 2008
Kman good observation of the ULL. That is a player down there.
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948. moonlightcowboy
9:55 PM CDT on May 27, 2008
Press, the twaves keep rolling this way.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
947. kmanislander
2:54 AM GMT on May 28, 2008
Hi Tampa

We have had the odd shower here and there over the last 5 days but no drought busters !

Still bone dry
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946. Drakoen
2:54 AM GMT on May 28, 2008
939. presslord 2:51 AM GMT on May 28, 2008
Is it safe to come in here and ask a tropical weather question?

ROFL.
Member Since: October 28, 2006 Posts: 57 Comments: 29919
945. presslord
2:53 AM GMT on May 28, 2008
With all the focus on the southern thingy, I'm curious....Is there anything particularly interesting happening in the Atlantic?
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944. TampaSpin
10:52 PM EDT on May 27, 2008
Hi Kman have you started getting any rain yet down there on a daily basis yet.
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942. weatherblog
2:51 AM GMT on May 28, 2008
I'm done for the night! Good discussions we had... later
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941. cdo
2:48 AM GMT on May 28, 2008
I am mostly a lurker on this blog...but I have a question...why do people use this blog as a subsitute for IM (conversations back and forth nothing to do with what Dr M's blog entry is about)? Also, as a mini personal blog so everyone will know how great or bad their day was (most dont care)?
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940. IKE
9:52 PM CDT on May 27, 2008
939. presslord 9:51 PM CDT on May 27, 2008
Is it safe to come in here and ask a tropical weather question?


LOL.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
939. presslord
2:49 AM GMT on May 28, 2008
Is it safe to come in here and ask a tropical weather question?
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938. kmanislander
2:45 AM GMT on May 28, 2008
890. Swells22 2:32 AM GMT on May 28, 2008
Hey can I get a little educated here as a tropical storm amateur? How can one tell a ULL from the vapor loop.

Upper level lows occur, as you might expect from the name, in the upper levels of the atmosphere. The water vapour loop is showing moisture in the atmosphere at those levels.

A low spins counterclockwise so a counterclockwise spin on the WV loop is a ULL because it is a low in the upper levels

This may not be a scientific explanation but it is the best I can do as a blogger !

Anyone else have a better explanation ?

It's just one of those things you learn to recognise when you see it
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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.