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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738. Tazmanian
6:20 PM PDT on May 27, 2008
when could we see 90L????
Member Since: May 21, 2006 Posts: 5091 Comments: 115131
737. extreme236
1:20 AM GMT on May 28, 2008
With the current direction of movement by 90E the GFS solution may not be wrong.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
736. extreme236
1:19 AM GMT on May 28, 2008
I guess we will just have to see what happens tomorrow with these two areas in the EPAC and Caribbean.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
735. extreme236
1:18 AM GMT on May 28, 2008
Continuing to develop and become even more impressive (STS Nakri)

Member Since: August 2, 2007 Posts: 19 Comments: 19234
734. hurricane23
9:17 PM EDT on May 27, 2008
726. Weather456 9:15 PM EDT on May 27, 2008
Eastern Pacific disturbance becoming better organize

http://www.ssd.noaa.gov/goes/east/watl/loop-ir4.html

TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM PDT TUE MAY 27 2008

SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A BROAD AREA OF LOW PRESSURE CENTERED A FEW HUNDRED MILES WEST OF COSTA RICA HAS BECOME A LITTLE BETTER ORGANIZED TODAY. SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF DAYS AS IT REMAINS NEARLY STATIONARY OR DRIFTS EASTWARD TO NORTHEASTWARD. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAINS ARE EXPECTED TO CONTINUE OVER PORTIONS OF PANAMA...COSTA RICA...AND NICARAGUA DURING THE NEXT DAY OR TWO.
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732. TerraNova
9:15 PM EDT on May 27, 2008
Thanks Storm.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
730. hurricane23
9:16 PM EDT on May 27, 2008
Rain for S.E. florida is a good bet as this entire area down in the SW carribean begins to lift northward in time.
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729. Tazmanian
6:13 PM PDT on May 27, 2008
no you are not . pearlandaggie


Michaael is # 20
Member Since: May 21, 2006 Posts: 5091 Comments: 115131
726. Weather456
9:06 PM AST on May 27, 2008
Eastern Pacific disturbance becoming better organize

http://www.ssd.noaa.gov/goes/east/watl/loop-ir4.html
Member Since: July 24, 2005 Posts: 407 Comments: 19076
725. WPBHurricane05
9:13 PM EDT on May 27, 2008
We used that magic button yesterday when his screen name was Michael. Now he's back again as Michaael.

The mods will probably ban his IP address if he keeps it up.


Back to the tropics.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
724. extreme236
1:12 AM GMT on May 28, 2008
he is #8 on my ignore list
Member Since: August 2, 2007 Posts: 19 Comments: 19234
723. zoomiami
1:12 AM GMT on May 28, 2008
I agree with WPB - feeding the trolls only encourages them.
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722. FLWeatherFreak91
9:12 PM EDT on May 27, 2008
717. WPBHurricane05 9:12 PM EDT on May 27, 2008 Hide this comment.
Do not feed the trolls.

Use the magic button.


We used that magic button yesterday when his screen name was Michael. Now he's back again as Michaael.
Member Since: Posts: Comments:
721. hurricane23
9:12 PM EDT on May 27, 2008
Development in the SW caribbean should slowly pick up late this week.

Iam sure its been posted but iam finding this getting kinda interesting.

CARIBBEAN...
A BROAD MONSOON GYRE LIES ACROSS THE FAR EASTERN PACIFIC...MUCH
OF CENTRAL AMERICA...AND OVER THE SW CARIBBEAN WITH THE ITCZ
AXIS SITUATED N OF PANAMA. SURFACE OBSERVATIONS FROM PANAMA
CITY...PUERTO LIMON...AND SAN ANDRES SUGGEST THAT A WEAK AREA OF
LOW PRES MAY BE LOCATED ALONG THE AXIS NEAR 10N81W BUT THE
SATELLITE REPRESENTATION IS STILL MOSTLY DISORGANIZED. AN UPPER
TROUGH AXIS EXTENDS FROM EASTERN CUBA ACROSS THE CAYMAN ISLANDS
TO BELIZE...WITH 50 KT W/SW UPPER LEVEL FLOW STREAMING ACROSS
THE CARIBBEAN AND DIFFLUENCE PRODUCING NUMEROUS MODERATE/
ISOLATED STRONG CONVECTION S OF 12N INTO PANAMA...COSTA
RICA...AND SOUTHERN NICARAGUA. DEEP MOISTURE WILL BEGIN LIFTING
N INTO THE NW CARIBBEAN OVER THE NEXT 24 HRS AS THE TROPICAL
WAVE NEAR 75W BEGINS TO INTERACT WITH THE SYSTEM.
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719. extreme236
1:10 AM GMT on May 28, 2008
713. Michaael 1:09 AM GMT on May 28, 2008
Point is....Let Mickey Mouse get blown around instead of gas prices


So basically your saying forget about the millions of people who live there and could die to just make a sacrifice and get over it. Wow that ignore button might get it's first use of the season.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
718. zoomiami
1:11 AM GMT on May 28, 2008
Hi Storm:

Reading your update, does this mean we're not going to get any rain in So Fla out of this?
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717. WPBHurricane05
9:11 PM EDT on May 27, 2008
Do not feed the trolls.

Use the magic button.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
716. pearlandaggie
1:10 AM GMT on May 28, 2008
am i on your list, Taz? ;)
Member Since: September 14, 2007 Posts: 3 Comments: 3963
714. Tazmanian
6:08 PM PDT on May 27, 2008
this added Ignore User #20 to my Ignore
Member Since: May 21, 2006 Posts: 5091 Comments: 115131
712. Skyepony (Mod)
1:07 AM GMT on May 28, 2008
It'll make for a fun night of blob watching. The MJO should add a bit of red to the rainbow tonight.
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711. extreme236
1:07 AM GMT on May 28, 2008
709. Michaael 1:06 AM GMT on May 28, 2008
Im not wishing on anybody. Im just saying if there is a big one, Florida has to take it, simple as that. I mean come on, what's in Florida besides retirees and mickey mouse runnin around, and people from FL always model watching when there aint nothing there!


If you wanting to get banned than your doing a great job!
Member Since: August 2, 2007 Posts: 19 Comments: 19234
708. Weather456
8:57 PM AST on May 27, 2008
656. extreme236 8:27 PM AST on May 27, 2008
Lots of active convection


MJO passing thru
Member Since: July 24, 2005 Posts: 407 Comments: 19076
707. extreme236
1:05 AM GMT on May 28, 2008
If Michaael lived in Florida he wouldn't be talking about "sacrifice" and be talking about wanting a cat 4 or 5 hurricane to hit Florida.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
706. WPBHurricane05
9:01 PM EDT on May 27, 2008
Still counting on their fingers aren't they? Lets see that's a cat 2 no wait a cat 3! no lets do a recount here.


Thats pretty funny, even though I lived in palm beach county during the 2000 election.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
705. Skyepony (Mod)
12:56 AM GMT on May 28, 2008
Looking at the spegetti models... the BamS has your more eastward track & the deep a westward. What this says is as long as it stays a shallow low near the surface & doesn't get strong the better a chance to go east. If it pulls together quick, then west ho & all Pacific event. It looks too big to gather quick & strong to me. It's not a tiny little thing that could be a cat 1 yet still shallow storm either.

I think still important is the interaction yesterday's backdoor cold front in FL is having on it, as well as how much draw the ULL E of FL may have on it.
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704. WPBCaneVet
9:04 PM EDT on May 27, 2008
700. Michael, you are one sick individual to wish a cat 4 or 5 on anyone. And to imply that the people of Florida deserve it is reprehensible.
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703. hahaguy
9:04 PM EDT on May 27, 2008
these are the prices of living in paradise
Member Since: August 12, 2007 Posts: 2 Comments: 2838
702. extreme236
1:02 AM GMT on May 28, 2008
Michaael I don't wish hurricanes on anybody and if I had to chose between Florida or Texas getting hit with a hurricane I wouldn't choose either. Sorry but you sound like a troll.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
701. StormHype
12:59 AM GMT on May 28, 2008
It is quite scary how on this show i am watching on channel 11 Accuweather news, They are stating that the NHC thinks within the very near future that a major hurricane will make its way through Tampa Bay....Our last major hurricane was in 1921. They are also stating this year could be the year.

Sounds like a desperate ,terror-based attempt for channel 11 to gain viewers in an era where more people are ditching TV weather for the web.... especially now that the web has decent video.
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699. CaneAddict
12:57 AM GMT on May 28, 2008
Also im surprised the local tampa mets are mentioning the models output with possible development in the Caribbean.
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698. extreme236
12:59 AM GMT on May 28, 2008
692. StormW 12:58 AM GMT on May 28, 2008
687. extreme236 8:55 PM EDT on May 27, 2008
Hey STORMKAT/STORMTOP's weather office just sent me a Weather Alert email saying his office predicts a Cat 5 NOLA hit...


Was it written in stone?

LOL!


LOL yea he was pretty sure about his prediction...I will keep you posted on any new alerts.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
697. juniormeteorologist
12:59 AM GMT on May 28, 2008
gfs model link please...
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695. TerraNova
8:58 PM EDT on May 27, 2008
Morning StormW

What is pushing 90E eastward and not westward?
Member Since: July 30, 2007 Posts: 76 Comments: 4063
691. pearlandaggie
12:57 AM GMT on May 28, 2008
690. you'd better watch that kind of talk before HouseOfGryffindor (sp.???) gets on you!
Member Since: September 14, 2007 Posts: 3 Comments: 3963
689. Skyepony (Mod)
12:49 AM GMT on May 28, 2008
000
NOUS42 KNHC 311400
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, TPC/NATIONAL HURRICANE CENTER, MIAMI, FL.
1000 AM EDT MON 31 MAR 2008
SUBJECT: WINTER STORM PLAN OF THE DAY (WSPOD)
VALID 01/1100Z TO 02/1100Z APR 2008
WSPOD NUMBER.....07-122

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.

3. NOTE: THIS IS THE LAST DAILY WINTER STORM PLANS OF
THE DAY, ANY SUBSEQUENT WILL ONLY BE PUBLISHED IF
THERE IS TASKING. THE NEXT SCHEDULED POD WILL BE 01 JUNE
WITH THE START OF THE TROPICAL SEASON.
WVW
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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.