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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1338. hugg70
1:06 AM GMT on December 31, 2009
There is no doubt that we are in a poeriod of globel climate warming. The grilla in the room is whether man has created it and if so to what extent. Perhaps a new bloog with some guys smarter than I.
1337. TheCaneWhisperer
4:18 PM GMT on May 28, 2008
1336. nrtiwlnvragn
4:16 PM GMT on May 28, 2008
New Blog
Member Since: September 23, 2005 Posts: 14 Comments: 11255
1334. powerofH2
4:13 PM GMT on May 28, 2008
Formerly H2Omaker, back again. I've been lurking and reading for the past 8 months since moving. No longer in the Houston area. I've moved to NW Louisiana now. My job is still water, but in a bit of a different sense. The power of hydrogen still drives the processes as it does in nearly all fluid processes and reactions.

I'm enjoying the reading and can now interject my comments and opinions. The tornado footage last week was amazing and appreciate those that posted the links.

BTW, to my eye it looks like we've got some splitting of the low(s) in the EPac and SW Carib. But I have to agree with 456, it appears that the total "draw" is to the Carib of all the energy. Time will tell.
1333. bystander
4:02 PM GMT on May 28, 2008
MLC,
Thanks for taking the time to do all of that. It is greatly appreciated. I have some studying to do on my lunch hour!
Member Since: July 24, 2007 Posts: 0 Comments: 201
1332. Cavin Rawlins
4:01 PM GMT on May 28, 2008
Hey guys....I just looked at a 30 frame water vapor loop of the West Atl/EPAC.....anyone notice an upper level cyclonic flow continues to dig across the Gulf and into the EPAC which is helping drive 90E towards the northeast. Its rather interesting to watch

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1331. moonlightcowboy
4:00 PM GMT on May 28, 2008
Bystander, no such thing as dumb questions, right? I ask them all the time, and I thank the good folks here for answering them - I've asked TONS.

The MJO is interesting. It can create additional moisture that aids in tropical development this time of year. I'll post this from the CPC and a couple of links so you'll get a better understanding. I'm still learning about it myself.

What is the Madden-Julian Oscillation (MJO)?
The Madden-Julian Oscillation (MJO) is a tropical disturbance that propagates eastward
around the global tropics with a cycle on the order of 30-60 days. The MJO has wide
ranging impacts on the patterns of tropical and extratropical precipitation, atmospheric
circulation, and surface temperature around the global tropics and subtropics. There is
evidence that the MJO influences the ENSO cycle. It does not cause El Nino or La Nina,
but can contribute to the speed of development and intensity of El Nino and La Nina
episodes.


MJO defined and characteristics.


MJO conditions and forecasts




I blogged on it a few weeks ago here.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1330. 0741
3:57 PM GMT on May 28, 2008
so rain that we were going to get here in miami got push into next week
1329. moonlightcowboy
3:51 PM GMT on May 28, 2008
323. Ivansrvivr 10:40 AM CDT on May 28, 2008
Shear is very low in the GOM but not nearly as low as atmospheric moisture content. The moisture that has filled in the Caribbean over the last 48 hrs. would have to spread northward into the GOM for a tropical system to have a chance to develop there.


...Amen!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1328. bystander
3:50 PM GMT on May 28, 2008
MLC,
I hope this is not a dumb question. I am trying to learn from all of you. What is the MJO pulse and what effect does it have on the tropics?
Member Since: July 24, 2007 Posts: 0 Comments: 201
1327. cchsweatherman
3:50 PM GMT on May 28, 2008
1323. Ivansrvivr 11:40 AM EDT on May 28, 2008
The E-Pac/Caribbean system looks to be splitting apart now. There is a definite circulation in the E-Pac but there are hints of a circulation in the SW Carib. Topography will assist anything developing in the SW Carib.

Shear is very low in the GOM but not nearly as low as atmospheric moisture content. The moisture that has filled in the Caribbean over the last 48 hrs. would have to spread northward into the GOM for a tropical system to have a chance to develop there.


That last part of your post depends upon how developed the tropical system would be at the time it would enter the GOM. Dry air is real damaging to developing systems, but if a system has already developed, it usually can produce its own moisture and dry air will not be a great inhibiting factor.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
1326. moonlightcowboy
3:49 PM GMT on May 28, 2008
Sporte, I'm ready, have car, have gas - WILL TRAVEL!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1325. moonlightcowboy
3:47 PM GMT on May 28, 2008


This shows the MJO pulse weakening.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1324. sporteguy03
3:44 PM GMT on May 28, 2008
MLC,
Should be interesting but are you prepared for Hurricane season?
Member Since: July 7, 2005 Posts: 0 Comments: 5399
1323. Ivansrvivr
3:40 PM GMT on May 28, 2008
The E-Pac/Caribbean system looks to be splitting apart now. There is a definite circulation in the E-Pac but there are hints of a circulation in the SW Carib. Topography will assist anything developing in the SW Carib.

Shear is very low in the GOM but not nearly as low as atmospheric moisture content. The moisture that has filled in the Caribbean over the last 48 hrs. would have to spread northward into the GOM for a tropical system to have a chance to develop there.
1322. StormJunkie
3:37 PM GMT on May 28, 2008
Morning SW :~)

Always a informative read!
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1319. StormJunkie
3:31 PM GMT on May 28, 2008
No need to apologize jp, I am always up for good healthy debate.

How all of us learn. Heck sometimes I play devil's advocate just so I can make sure there is nothing I am missing on the other side of what I perceive to be going on.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1317. moonlightcowboy
3:31 PM GMT on May 28, 2008
And, that also reiterates what K'man has been saying, too - any development will be slow, especially considering 90E consuming energy and any land interaction, not to mention nCarib forecasts of increased shear. However, WU's shear map indicates shear may become more favorable.



I'm thinking 90E will strengthen somewhat, possibly get named, eventually moving n, wnw, nw, and then dissipate with land interaction.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1313. franck
3:29 PM GMT on May 28, 2008
This time of year it doesn't take as much wind to break up a developing system. Actually, it would be great for a tropical system to form and bring soaking rains to a large area of the SE, even if there were some accompanying winds. But it probably won't happen. Nothing coming to the 'gigante del norte'.
Member Since: August 30, 2005 Posts: 0 Comments: 1150
1311. StormJunkie
3:28 PM GMT on May 28, 2008
Well then there is no debate...lol :~)

That area is a slow roller and it will just have to fester for a while if anything is to come of it.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1310. guygee
3:26 PM GMT on May 28, 2008
The WV loops show an upper level trough working its way along the backside (west) of the ULH over 90E. This shows up in the CIMMS 200mb Relative Vorticity Analyses as well. The interaction with the trough is expanding the ULH NE into the Caribbean, where some impressive upper level divergence is combining with low-level convergence in the vicinity of broad low pressure at the surface.

I will not be surprised to see 90E come ashore on the W. Coast of Costa Rica within the next 24 hrs, with the possibility on a new surface low center forming in the SW Caribbean. What happens after that remains to be seen (a bridge too far for my tastes).

BBL.
Member Since: September 16, 2005 Posts: 0 Comments: 3174
1309. IKE
3:25 PM GMT on May 28, 2008
And the high is suppose to break down by next week over the SE USA......

From the Mobile,AL morning discussion...long-term.....

"The airmass will be fairly capped off through
much of the weekend. We bring the slight chance probability of precipitation back into the
picture in the early next week as a weakness is projected to form on
the east side of the upper ridge
...giving a somewhat greater
potential for any mesoscale system developing along the southern
edge of the stronger midlevel westerlies to come down the
northwesterly flow aloft into Mississippi and Alabama."
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1307. cchsweatherman
3:24 PM GMT on May 28, 2008
Never mind nrtiwlnvragn. That is Pacific standard time, not Eastern standard time. Made a mistake.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
1306. nrtiwlnvragn
3:23 PM GMT on May 28, 2008
1304. cchsweatherman

That is PDT not EDT, 11AM PDT - 2PM EDT
Member Since: September 23, 2005 Posts: 14 Comments: 11255
1304. cchsweatherman
3:22 PM GMT on May 28, 2008
Here is the link nrtiwlnvragn.
Link
Member Since: April 14, 2007 Posts: 8 Comments: 5169
1303. StormJunkie
3:21 PM GMT on May 28, 2008
On the models: 2 of the computer models (NOGAPS and
GFS) still show some development in the western
Caribbean, however have pushed this back until the
first week of June. The NOGAPS brings a Tropical
Storm up to the Yucatan Channel at 144 hours out, and
the GFS brings the system over SE FL late in the first
week of June. I cannot rule this out completely at
this time, as some of the computer models do reduce
wind shear around that time to marginal to slightly
favorable levels close to the end of that time frame.
As far as any development in the western Caribbean
within the next few days...it is slim at this
time...as with the EPAC system so close, the outflow
from the upper levels will have a tendency to stifle
anything in the western Caribbean. I will continue to
monitor this area over the next week.
-StormW

jp, you say the voice of reason, but I think this is exactly what GS and myself were referring to. So now I am even more confused as to what we are debating?
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1302. nrtiwlnvragn
3:21 PM GMT on May 28, 2008
1300. cchsweatherman

Which graphic is that?
Member Since: September 23, 2005 Posts: 14 Comments: 11255
1300. cchsweatherman
3:20 PM GMT on May 28, 2008
1299. nrtiwlnvragn 11:18 AM EDT on May 28, 2008
1288. cchsweatherman

TWD and TWO are now issued at synoptic time, 8Am, 2PM, 8PM, 2AM.


Well, the NHC has to update their graphic indicating that they have updates a 5AM, 11AM, 5PM, and 11PM.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
1299. nrtiwlnvragn
3:18 PM GMT on May 28, 2008
1288. cchsweatherman

TWD and TWO are now issued at synoptic time, 8Am, 2PM, 8PM, 2AM.
Member Since: September 23, 2005 Posts: 14 Comments: 11255
1298. StormJunkie
3:16 PM GMT on May 28, 2008
Not sure I understand the question jp.

I have seen centers relocate, and coexist for a short period of time. Especially in broad weak systems (what we have).

And again, I am not looking for any development today or tomorrow. 90e moving inland would change the dynamics of the Carib side considerably as it weakens and dissipates. I am also not saying a system will develop on the Atl side, just saying it is not out of the realm of possibility. Just going to take time if it does.

Again, no instant gratification. Pretty swirl down there; but it is a wait and see system. As most are.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1296. OUSHAWN
3:15 PM GMT on May 28, 2008
JP,

I have to respectfully disagree with you. I see a seperate circulation going on in the SW Caribbean. If you look right near land you can see there is definite smaller turning going on there on the Caribbean side. I could be wrong but looks to me like that is what is going on.

Shawn
Member Since: September 20, 2007 Posts: 0 Comments: 44
1295. cchsweatherman
3:14 PM GMT on May 28, 2008
1289. kmanislander 11:10 AM EDT on May 28, 2008
There is another possibility as well

The rotation of 90E might be inducing a high over the S Caribbean due to the counterclockwise rotation in the EPAC with winds coming up from the South and fanning out to the NE


That is sone excellent thinking there. Never thought about that. Definitely something to consider and monitor. See, this is why I come here to these blogs; they offer so many insights and opinions that you're bound to learn something new or have your views changed as you become more aware of the global perspective.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
1294. IKE
3:13 PM GMT on May 28, 2008
Managua, NK (Airport)
Updated: 13 min 3 sec ago
Scattered Clouds
82 °F
Scattered Clouds
Humidity: 70%
Dew Point: 72 °F
Wind: 7 mph from the ENE
Pressure: 29.77 in (Steady)
Heat Index: 87 °F
Visibility: 6.2 miles
UV: 8 out of 16
Clouds:
Scattered Clouds 2000 ft
Scattered Clouds 7000 ft
(Above Ground Level)..............

Nicaragua
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1290. StormJunkie
3:10 PM GMT on May 28, 2008
Buhdog,

Forecast Model Pages

And some video tutorials on how to navigate some of the model pages.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
1289. kmanislander
3:10 PM GMT on May 28, 2008
There is another possibility as well

The rotation of 90E might be inducing a high over the S Caribbean due to the counterclockwise rotation in the EPAC with winds coming up from the South and fanning out to the NE
Member Since: August 19, 2006 Posts: 0 Comments: 15846
1288. cchsweatherman
3:09 PM GMT on May 28, 2008
Watching the latest RAMSDIS loops, it appears that the low-level circulation has really started to tighten as convection continues to organize and consolidate around the center. Quite an impressive system.

By the way, doesn't the NHC issue a Tropical Weather Outlook every six hours for the Eastern Pacific? Still have no update from the NHC.
Member Since: April 14, 2007 Posts: 8 Comments: 5169

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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.

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