Is U.S. climate getting more extreme?

By: Dr. Jeff Masters , 1:54 PM GMT on March 13, 2009

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Is the climate in the U.S. getting more extreme? The answer to this question depends upon how one defines "extreme". For example, the number of extreme tornadoes (violent EF-4 and EF-5 twisters) has not increased in recent years. We lack the data to judge whether there has been an increase in severe thunderstorms and hail. There has been a marked increase in Atlantic hurricane activity since 1995 (though the possible contribution of human-caused global warming to this increase is not something hurricane scientists agree upon). Since it is difficult to quantify how severe storms like tornadoes and hurricanes are changing, a better measure of how climate extremes are changing is to look at temperature and precipitation, which are well-measured. NOAA's National Climatic Data Center (NCDC) has developed a Climate Extremes Index to attempt to quantify whether or not the U.S. climate is getting more extreme. The Climate Extremes Index (CEI) is based upon three parameters:

1) Monthly maximum and minimum temperature
2) Daily precipitation
3) Monthly Palmer Drought Severity Index (PDSI)

The temperature data is taken from 1100 stations in the U.S. Historical Climatology Network (USHCN), a network of stations that have a long period of record, with little missing data. The temperature data is corrected for the Urban Heat Island effect, as well as for station and instrument changes. The precipitation data is taken from 1300 National Weather Service Cooperative stations. The Climate Extremes Index defines "much above normal" as the highest 10% of data, "much below normal" as the lowest 10%, and is the average of these five quantities:

1) The sum of (a) percentage of the United States with maximum temperatures much below normal and (b) percentage of the United States with maximum temperatures much above normal.

2) The sum of (a) percentage of the United States with minimum temperatures much below normal and (b) percentage of the United States with minimum temperatures much above normal.

3) The sum of (a) percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the Palmer Drought Severity Index (PDSI) and (b) percentage of the United States with severe moisture surplus (equivalent to the highest tenth percentile) based on the PDSI.

4) Twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events.

5) The sum of (a) percentage of the United States with a much greater than normal number of days with precipitation and (b) percentage of the United States with a much greater than normal number of days without precipitation.


Figure 1. The Annual Climate Extremes Index (CEI), updated through 2008, shows that U.S. climate has been getting more extreme since the early 1970s. Image credit: National Climatic Data Center. On average since 1910, 20% of the U.S. has seen extreme conditions in a given year (thick black line).

As summarized by Gleason et al. (2008), the National Climatic Data Center concludes that based on the Climate Extremes Index, the percentage of the U.S. seeing extreme temperatures and precipitation generally increased since the early 1970s. These increases were most pronounced in the summer. No trend in extremes were noted for winter. The annual CEI index plot averaged for all five temperature and precipitation indices (Figure 1) showed that five of the fifteen most extreme years on record occurred since 1997. Shorter-lived periods with high CEI values occurred in the 1930s and 1950s, in association with widespread extreme drought and above-average temperatures. The most extreme year in U.S. history was 1998, with 1934 a close second. The year 1998 was the hottest year in U.S. history, with a record 78% of the U.S. experiencing minimum temperatures much above normal. That year also had a record 23% of the U.S. with much greater than normal precipitation from extreme 1-day precipitation events. The 1934 extreme in CEI was due in large part because of the most widespread drought of the century--a full 52% of the U.S. was affected by severe or extreme drought conditions. That year also saw a record 64% of the U.S. with much above normal maximum temperatures.

The impact of maximum and minimum temperatures on the Climate Extreme Index
It is very interesting to look at the five separate indices that go into the Climate Extremes Index. Today I'll look at temperature, and next week, I'll focus on drought and precipitation. The portion of the U.S. experiencing month-long maximum temperatures either much above normal or much below normal has been about 10% over the past century (black lines in Figure 2). However, over the past decade, about 20-25% of the U.S. has been experiencing monthly maximum temperatures much above normal, and the portion of the U.S. experiencing much colder than normal high temperatures has been near zero. Minimum temperatures show a similar behavior, but have increased more than the maximums (Figure 3). Over the past decade, minimum temperatures much above normal have affected 25-35% of the U.S. This means that the daily range of temperature (difference between minimum and maximum) has decreased over the past decade, which is what global warming says should be happening if greenhouse gases are primarily to blame for the rise in temperatures.

While there have been a few years (1921, 1934) when the portion of the U.S. experiencing much above normal maximum temperatures was greater than anything observed in the past decade, the sustained lack of maximum temperatures much below normal over the past decade is unique. The behavior of minimum temperatures over the past decade is clearly unprecedented--both in the lack of minimum temperatures much below normal, and in the abnormal portion of the U.S. with much above normal minimum temperatures. Remember that these data ARE corrected for the Urban Heat Island effect, so we cannot blame increased urbanization on the increase in temperatures. Recall that the all-time record maximum and minimum temperature data, which I presented in a post in February, are not corrected for the Urban Heat Island Effect, but look very similar to the CEI maximum and minimum temperature trends presented here.

A lot of people have told me that they believe we are experiencing more wild swings of temperature from hot to cold from day to day in recent years, but the CEI data does not answer this question. To my knowledge, a study of this kind has not been done.


Figure 2. The Annual Climate Extremes Index (CEI) for maximum temperature, updated through 2008, shows that 20-25% of U.S. has had maximum temperatures much above normal over the past decade. Image credit: National Climatic Data Center.


Figure 3. The Annual Climate Extremes Index (CEI) for minimum temperature, updated through 2008, shows that 25-35% of U.S. has had minimum temperatures much above normal over the past decade. Image credit: National Climatic Data Center.

References
Gleason, K.L., J.H. Lawrimore, D.H. Levinson, T.R. Karl, and D.J. Karoly, 2008: "A Revised U.S. Climate Extremes Index", J. Climate, 21, 2124-2137.

Annual WeatherDance contest ready for registration!
Armchair forecasters, now's your chance to shine! WeatherDance, based on teams in the men's and women's NCAA basketball tournaments, allows players to predict which team's city will be hotter or colder on game day in each round of the Big Dance. Beginning today, players can make their forecasts at the Weather Dance Web site at: www.weatherdance.org. The site will be updated with cities promptly after NCAA seeding announcements. First round Weather Dance selections must be entered by 11:59 p.m. EDT Wednesday, March 18.

"Officially, Weather Dance began as a class project to get students involved in weather forecasting, but we kept it around because it got popular. People think they can do better forecasting than the meteorologists. Well, here's their shot!" said Perry Samson, WeatherDance creator, co-founder of the The Weather Underground, Inc., and Professor in the Department of Atmospheric, Oceanic and Space Sciences at the University of Michigan.

This is the fifth year for the game. Last year more than 2,000 people played. Most play merely for the thrill, but many K-12 science teachers involve their classes as part of meteorology units. The winning teacher will receive an expense-paid trip to join the Texas Tech/University of Michigan Storm Chasing team this spring for a day of tornado chasing in Tornado Alley. Other winners will receive a Weather Underground umbrella, "Extreme Weather" mugs, or a copy of the book "Extreme Weather," by Christopher C. Burt.

I'll talk about drought and precipitation trends in my next post, Monday or Tuesday.

Jeff Masters

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75 days till Hurricane season.
Member Since: July 8, 2005 Posts: 259 Comments: 24575
Quoting vortfix:
Hey Flood!
Nice to see you.
Now please send a little moisture down Florida way.

We just added two more counties above the 700 mark today:






A large, stalled out TS would take care of this.
Member Since: July 8, 2005 Posts: 259 Comments: 24575
I'll say one thing when I was down on the gulf side last week,went in swimming a couple of times,and pretty easy to tell it was a cold winter,that water was pretty cold.
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Quoting RitaEvac:
Florida drought, TX drought, maybe the 2 states that get hit by the big ones this year...
Gosh thanks so much for the good wishes Ritaevac. the rain here was welcome over the weekend but we need more soon. I would prefer it a bit warmer when it rains however.
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Florida drought, TX drought, maybe the 2 states that get hit by the big ones this year...
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Hello everyone......i am hosting a Basketball Pool event for Charity for Portlight. All the info is on my Web Site.

TampaSpins Web Link
Member Since: September 2, 2007 Posts: 179 Comments: 20448
NEW OUTLOOK POSTED:
South Florida StormWatch
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Saw some convection to the east SRQ -- keep hoping

Link
Member Since: June 12, 2005 Posts: 6 Comments: 8188
NE, ya you can't even find a house that has a yard that is green it's all brown here.
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412.

That sounds like us...we got rained on but good last week, but were under fire warning the week before that...the humidity drops, the wind turns to the SW and the brush turns into tinder
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haha,was down there last week, and couldn't believe how dry you guys are,they had to close highway 75 for a while due to a wild fire.
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410. Skyepony (Mod)
Cpc's monday ENSO update is out. Region 3,4 is up to -.4 that makes neutral conditons~ not offically cause we need 3 months average above -.5, of course. But the 1st we've seen neutral at all since like last fall. ESPI is -1.66 & region 3 has fallen to -.8 so I really expect region 3,4 to slip again back into La Niña conditions next week. If it decides to stay, we will see. I had full on expected to see a steady climb to Neautral, which is what happened but now the ESPI has turned very negative suddenly.
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vortfix lets hope that the front doesn't dry up before it gets here in south florida.
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407.

Yep, those folks down south got it pretty bad...again, it could have been a lot worse; Ike didn't live up to his full potential. As for us here in DFW, we got nothgin from Ike at all, but we did get a little ice over the winter
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floodman, was not fun this winter,still a little ways to go,but compared to what you guys went through,I can live with my winter.
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vort, if I could, I certainly would...good seeing you!
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Getting there, Newx. How are things in the great NE? You guys got hammered this winter, huh?
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Nice to see ya,floodman,hope things have settled down for you there.
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tkeith, how you doing?

Hydrus, you have mail
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Good to "see" you again Floodman...
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FLOOD MAN-It has been a while since i have seen you post.If you have time,please tell me where you are and what happened to you last year.
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As ready as I'll ever be, I guess...LOL

Looks like it may be another interesting year, ENSO wise at least
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I've been good , ready for season 09? lol
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Yeah, cleaning up after storm season '08. How've you been?
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Hey floodman , it's been a while
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Howdy folks...been a while
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394. JRRP
near 10n 45w still warm a bit
Link
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393. HadesGodWyvern (Mod)
Joint Typhoon Warning Center

Tropical Cyclone Formation Alert (1300z 16MAR)
============================================
An area of convection (95P) located at 18.9S 163.2W or 240 NM northwest of Rarotonga, Southern Cooks Island. Animated infrared satellite imagery and a 0803z METOP-A image indicates a rapidly consolidating low level circulation center with multiple deep convective bands spiraling into the center. This system, like TC Joni, is developing from the mid-levels down to the surface. However, unlike Joni, this system has better radial outflow with more rapidly improving convective banding evident at this early stage of development. Despite surface development lagging slightly behind convective organization, Scatterometer data has increasingly supported a strengthening low level circulation center. A partial 0805z ASCAT image shows 25-30 knot northerly floe over the eastern semi-circle. These winds were verified by a 0000z ship observation from MYMXS of 22 knots. The overall environment is very favorable for further development. Upper level analysis and animated water vapor imagery indicates an anticyclone over the low level circulation center with very good poleward outflow enhanced by two upper level lows (one southeast and another one southwest of the system), as well as excellent equatorward outflow enhanced by strong cross-equatorial flow. The sea surface temperatures is around 29C. Ocean heat content and a deep moisture envelope (greater than 60MM) support continued consolidation.

Maximum sustianed winds near the center is 25-30 knots with a minimum sea level pressure of 1000 MB. Based on the favorable environment characterized by excellent outflow and a rapidly organizing low level circulation center, the potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is UPGRADED TO GOOD.
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Quoting Ossqss:


Is this like pushing the reset button?


I think its just saying that we may be trying to make a mountain out of a molehill
Member Since: October 1, 2007 Posts: 81 Comments: 26516
Quoting Orcasystems:
UW-Milwaukee Study Could Realign Climate Change Theory

Now the question is how has warming slowed and how much influence does human activity have?

"But if we don't understand what is natural, I don't think we can say much about what the humans are doing. So our interest is to understand -- first the natural variability of climate -- and then take it from there. So we were very excited when we realized a lot of changes in the past century from warmer to cooler and then back to warmer were all natural," Tsonis said.


Is this like pushing the reset button?
Member Since: June 12, 2005 Posts: 6 Comments: 8188
UW-Milwaukee Study Could Realign Climate Change Theory

Now the question is how has warming slowed and how much influence does human activity have?

"But if we don't understand what is natural, I don't think we can say much about what the humans are doing. So our interest is to understand -- first the natural variability of climate -- and then take it from there. So we were very excited when we realized a lot of changes in the past century from warmer to cooler and then back to warmer were all natural," Tsonis said.
Member Since: October 1, 2007 Posts: 81 Comments: 26516
GM all,spent last week in the wonderful state of Florida,and want to thank you all for picture perfect weather,which is not good for your drought,but back to Mass. and heavy clothes,but no snow.
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Quoting ftpiercecane:


Yeah, a friend of mine just took a job transfer from the east coast of florida to anchorage. He doesn't leave for a couple of weeks, and I just sent him a link of redoubt off of fox news to make him feel better.
that's what friends are for...LOL!
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Certainly drought conditions here in East Central Florida. I fill up two large waterbowls in my yard every night and every morning they're empty. Also make sure the water by my feeder stays full. Our creatures need water, too!
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Quoting tkeith:
Looks like Redoubt is getting seriousLink


Yeah, a friend of mine just took a job transfer from the east coast of florida to anchorage. He doesn't leave for a couple of weeks, and I just sent him a link of redoubt off of fox news to make him feel better.
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Good morning everyone. Lots of good information and discussion this morning. Spent the weekend working in the town of Sikeston, Missiouri where ice storms broke off limbs from virtually every tree in town. Streets were so plugged with debris they were impassible until time to clear them - but took some amazing pictures of trees with whole tops broken off, yet below them were branches in full bloom with gorgeous flowers - Really cool metaphor for what always seems to happen after a storm - we move past the damage and spring happens. Pray for rain for the Lady in Red. I sure wouldn't wanted to be surrounded by fields of dry grass and forest.
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Looks like Redoubt is getting seriousLink
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Morning..........Based on current ENSO information, it looks to be in a neutral phase going into H-Season............
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Quoting charlottefl:
Musta missed my comment the other day. Lady is red is having pink flahses..;)



didn't miss it... let's hope she don't HOTFLASH..

after watching those AussieVideo of their fire's -- I'm very edgy -- I know what can happen and the the fuel is out there. One day won't do it as the rain will mostly "run-off" we need several three day soakers w/no lightening.... just to begin to extinguish the problem
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Just to comment on the whole SST issue. The Atlantic, Gulf and Caribbean all warm rapidly during the month of May, so I wouldn't put too much into the SST's in the ATL now. I'm curious to see some SAL forecasts for the summer. That does have some ability to limit sea temp rise along with other factors.
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Musta missed my comment the other day. Lady is red is having pink flahses..;)

Quoting surfmom:
Florida continues to wear red on the Fire/drought maps.... today she is sporting a fuchsia center................

Been asking Mother Nature to give us some rain here.... I am on her IGNORE LIST.
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Florida continues to wear red on the Fire/drought maps.... today she is sporting a fuchsia center................

Been asking Mother Nature to give us some rain here.... I am on her IGNORE LIST.
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Quoting KoritheMan:


As I said, it won't take long to warm up once consecutive periods of heat build in -- not long at all. I've seen this happen year after year.


Even though I respectfully disagree with you on activity picking up early, I can't say you are wrong because I have already seen so many crazy things happen in the Atlantic in the few years I have been around.
However if the SST's continue warming at they rate they are a may need to make a revision to my forecast.
Member Since: September 7, 2008 Posts: 17 Comments: 1604
376. HadesGodWyvern (Mod)
Joint Typhoon Warning Center

Tropical Disturbance Summary (0800z 16MAR)
========================================
An area of convection (95P) located at 18.1S 163.1W or 270 Nm northwest of Rarotonga, Southern Cooks Islands. Animated multispectral satellite imagery depicts a rapidly consolidating defined low level circulation center. A 0511z SSMI 37ghz image shows multiple convective bands wrapping into the center. Upper level analysis and animated water vapor imagery indicates an anticyclone over the low level circulation center with very good poleward outflow enhanced by two upper level lows (southwest and southeast of the system), as well as excellent equatorward outflow enhanced by strong cross-equatorward flow.

Maximum sustained winds near the center is 20-25 knots with a minimum sea level pressure of 1004 MB. Based on the favorable environment charcterized by excellent outflow and rapidly organizing low level circulation center, the potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is FAIR.
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Quoting SevereHurricane:


The water is cooler than it was this time last year.


As I said, it won't take long to warm up once consecutive periods of heat build in -- not long at all. I've seen this happen year after year.
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Quoting hurristat:


Have you seen the water south of Panama? There is a 90F spot surrounded by 60F water...lol


I've seen that occurrence for a few years. I wonder what it is... But here are the aforementioned below average Caribbean SSTs that I mentioned:



Also, as previously mentioned, Gulf SSTs are currently running above average, save for in the eastern and extreme southern portion. Of course, the talk of March SSTs is meaningless, because as I told Baha, once warm to hot temperatures roll in for a prolonged period, it doesn't take long for the water to heat up -- this happened in June 2007 when the entire Gulf went from below average to 1 to 2C above average.
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359. Orcasystems 11:45 PM EDT on March 15, 2009

Thanks for the graph.
1955 being a cold year explains my existence!
Must have started with a cold January.
I was born in September of that year.

LOL!
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I've been off most of the winter
over at Sully's blog to watch the northeast.

Won't be long before we see some tropical events again though, eh?

I'll be around.
Thanks for keeping this blog going
Doc Masters...and all of you...!
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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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