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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Yep so if things hold up looks like we are in for a very active season.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
470. HadesGodWyvern (Mod)
Fiji Meteorological Services
Tropical Disturbance Summary
TROPICAL DEPRESSION TWELVE-F
9:00 AM FST March 17 2009
========================================

At 21:00 PM UTC, Tropical Depression 12F [1002 hPa] located at 21.0S 163.1W is reported as slowly moving. Position POOR based on multispectral infrared/visible imagery with animation and latest Quikscat Pass.

Deep convection has erupted close to the low level circulation center. excellent diffluence over the system is supporting feeder bands around the system. The system lies under a mid level short wave trough. Mid level ridge to the east is expected to steer the system southwards.

Global models support further intensification of TWELVE-F. ECMWF indicates an amplifying thermal trough to the west of TWELVE-F and this is expected to deepen the system rapidly in the next 24 hours.

POTENTIAL FOR 12F TO DEVELOP INTO A TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS MODERATE TO HIGH.
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469. Skyepony (Mod)
It's Neutral now... Today's CPC numbers had region 3,4 at -.4. With region 3 down to -.8 & the ESPI at -1.66 I suspect very soon it will be La Niña conditions again. ESPI has done an about face & more so than just the effects of the last Kelvin wave.
Member Since: August 10, 2005 Posts: 178 Comments: 38310
Quoting StSimonsIslandGAGuy:
It's been Georgia's turn for about 80 years.....
Yep, you are so right, St.SimonsIslandGAGuy, Georgia experienced three major hurricanes in the later half of the 19th Century: a Category 3 in 1854 near Savannah, the Category 3 "Sea Islands Hurricane" in 1893 that killed 1000-2000 people near Savannah and a Category 4 in 1898 near Brunswick.

Hurricane Would Cause Huge Floods For Ga. Coast
"The Georgia coastline is one of the most surge-prone areas in the country. It's very surge-prone in Savannah, much more so than in Charleston. So, if the same hurricane that hits Charleston, it will do much worse damage waterwise in Savannah than it will in Charleston," said Dr. Lyons.

A major hurricane would cause a storm surge of perhaps 30 feet, bringing flood waters more than 15 miles inland.


Member Since: August 19, 2008 Posts: 6 Comments: 2490
Okay teddy I am going to go bury my head in the sand now that you said that.
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Looks colder in the East pacific than it did a couple weeks ago, especially at the Equator. There was some pretty deep Reds off Africa too not to long ago. Should start creeping to the Caribbean soon.
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Seems folks in the south have 2 good reasons to get rid of the dead wood.
1)Fire control
2)Preparation for Hurricane season


Member Since: August 19, 2008 Posts: 6 Comments: 2490
what is the information coming out about the high vs low of the SST's this year?
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I know they are the great equalizers, but whats the percentage increase for areas that have droughts to have a greater or lesser chance of a major storm impacting them?

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Quoting StSimonsIslandGAGuy:
It's been Georgia's turn for about 80 years.....


Georgia has not expirienced a Major Hurricane Landfall in 116 years...
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Quoting BahaHurican:
Hey,23. Someone was suggesting last night that we likely won't go to neutral conditions until about 1/2 way into the season, using that same diagram. I'm still not convinced that we will see any serious SST warming anomalies this year, given the current ENSO forecast. I'm thinking about this more in terms of where more powerful storms are likely to occur and be sustained.

Anybody else thinking a relatively slow season for EPac?


I said we should be in neutral conditions by the climax of the season.
I am certian will be in Neutral by mid-July.
But we will be in the Warm Side of Neutral in September.
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Quoting hurricane23:
Afternoon....

Based on this map of Dynamical/Statistical models my guess is la nina could very well hang on a tad longer then currently forcasted and go neutral for the heart of the season. Adrian



Yea I see we are on the same page,
Psted the same lovley chart on the previous page.
Looks to me like 2009 may be a beast.
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I am hosting a Charity Event for Portlight with a Tournment Pool. If anyone would like to Join it will be alot of fun and for a good cause. Please help out if you can.

March Madness Charity Event Link
Member Since: September 2, 2007 Posts: 178 Comments: 20443
457. HTV
Quoting plywoodstatenative:
homeless I hate to say this, you all had Ike last year. That was supposed to be our system, something tells me its our turn. However What is the link between droughts and major hurricanes?

Ask any of the old-timers(I guess I may be in that camp) on the Gulf Coast and they will tell you that ts's and hurricanes are the great equalizers.
Quoting plywoodstatenative:
homeless, pull up the South Florida water management page. Look at the link entitled Weather. There is a huge amount of rain up north of us.

However it appears that an early Bermuda High has set itself in place off the coast of South Florida.
I saw the graphic with all the purple. Hopefully that high will break down soon.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
plywood, I'm thinkin' La nina changes storm track patterns, too, correlating with more systems heading due west rather than NW. U realize that aside from Fay and Hanna, FL and the NW Bahamas received practically no TC based weather? Even Twaves and depressions seemed to skirt us this year.

I have a feeling that with a return to ENSO neutral conditions we may find ourselves back in the more "normal" pattern of regular rain from tropical disturbances.

Of course, doesn't do much right now. . . .
Member Since: October 25, 2005 Posts: 19 Comments: 22357
Its really unusual for us to have a high off the coast that is as strong as this one is. Thats the main reason that we have had as much trouble with rain than anything else. Just sitting there pumping more and more dry air over us and killing any chances of that rain maker over north florida coming this way.
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homeless, pull up the South Florida water management page. Look at the link entitled Weather. There is a huge amount of rain up north of us.

However it appears that an early Bermuda High has set itself in place off the coast of South Florida.
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Quoting plywoodstatenative:
homeless I hate to say this, you all had Ike last year. That was supposed to be our system, something tells me its our turn. However What is the link between droughts and major hurricanes?
I hope nobody gets a big one. But,if I'm right, Ike came this way because of the high over Florida. Hopefully that won't set up again. I know y'all need the rain.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
yeah, but what does that do for us in the ole hurricane alley?
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After days and days of steady rain SETX is now only in a moderate drought. Lot worse just to our west though. But we are unusually dry. Last week I saw my first fire warning ever. Unbelievable low humidity around here. And theres a lot of dead vegetation too.
Member Since: August 15, 2008 Posts: 10 Comments: 3665
During LaNina

Mid-latitude low pressure systems tend to be weaker than normal in the region of the Gulf of Alaska, during a cold episode winter. This favors the build-up of colder than normal air over Alaska and western Canada, which often penetrates into the northern Great Plains and the western United States. The southeastern United States, on the other hand, becomes warmer and drier than normal.

Member Since: September 2, 2007 Posts: 178 Comments: 20443
homeless I hate to say this, you all had Ike last year. That was supposed to be our system, something tells me its our turn. However What is the link between droughts and major hurricanes?
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After reading its just the opposite....dumb me...Florida would be dry during LaNina. So its doing exactly as!
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting hurricane23:
Afternoon....

Based on this map of Dynamical/Statistical models my guess is la nina could very well hang on a tad longer then currently forcasted and go neutral for the heart of the season. Adrian

Hey,23. Someone was suggesting last night that we likely won't go to neutral conditions until about 1/2 way into the season, using that same diagram. I'm still not convinced that we will see any serious SST warming anomalies this year, given the current ENSO forecast. I'm thinking about this more in terms of where more powerful storms are likely to occur and be sustained.

Anybody else thinking a relatively slow season for EPac?
Member Since: October 25, 2005 Posts: 19 Comments: 22357
Taz am i correct about the LaNina for Florida.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Quoting RitaEvac:
Florida drought, TX drought, maybe the 2 states that get hit by the big ones this year...

No Thank You! 4 Storms 3 hurricanes in 3 years. Ive had my fill. LOL
Member Since: August 15, 2008 Posts: 10 Comments: 3665
Quoting plywoodstatenative:
Tampa, I can not remember a time when it was this bad rain wise. I mean we got about a minutes worth of rain yesterday morning. And nothing since then. Dark rain clouds this morning, but nothing except lightning of course. Now its smoky as heck cause of a fire north of us in Palm Beach.


If i remember correct in La Nina we should be cooler and wetter than normal.....we was cooler but, the wetter did not happen....strange.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
taz, I will take anything that can sit ontop of southern florida and dump rain on us. Anything short of a major storm right now.
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like TS fay
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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:








we????
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Tampa, I can not remember a time when it was this bad rain wise. I mean we got about a minutes worth of rain yesterday morning. And nothing since then. Dark rain clouds this morning, but nothing except lightning of course. Now its smoky as heck cause of a fire north of us in Palm Beach.
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Cybr, remember thats the OFFICIAL start. Mother nature usually starts it up earlier than that and the way our weather patterns are I have a gut feeling that it will start up in the mid of June or so.
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The GFS and Nam has the Rain in Florida drying up since the last runs......:(



Member Since: September 2, 2007 Posts: 178 Comments: 20443
adrian, so a neutral La Nina would do what for us???
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Quoting philliesrock:

The winter ENSO state was forecasted to be neutral by a number of people...I expect La Nina to hold on a little longer. From past experience it doesn't go away that easily.


Also, it takes several days before any thing changes in the Atlantic.
Member Since: September 2, 2007 Posts: 178 Comments: 20443
Of course we had rain clouds, but nothing much happened in the way of moisture. Of course mother nature did start up some fires, but other than that, well that sums up what has been going on in Broward county as of late.

Vort, that map of yours says it all. The question I have is this: With two dry rainy seasons in a row, does that imply anything towards hurricane season as well as an unusually dry winter?
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Quoting hurricane23:
Afternoon....

Based on this map of Dynamical/Statistical models my guess is la nina could very well hang on a tad longer then currently forcasted and go neutral for the heart of the season. Adrian


The winter ENSO state was forecasted to be neutral by a number of people...I expect La Nina to hold on a little longer. From past experience it doesn't go away that easily.
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Here is the latest Cape Values...

Member Since: September 2, 2007 Posts: 178 Comments: 20443
431. HTV
Quoting CybrTeddy:


Actually don't, with this drought think slow moving TS

Sorry my bad. It rained here the last four days but barely got an inch in my bucket. NWS at Busch Int. says we are only about 7 inches behind since Ike, but you go in most any direction a few miles and the average is a 12-13 inches behind. I'm thinkin' one of them Longhorn Steers must of peed in the bucket, or maybe it's those United Airlines Pilots. We keep our fingers crossed for some more stalled fronts.
Quoting CybrTeddy:


Actually don't, with this drought think slow moving TS


A TS will be months away. We need one more slow cold front, soon, to bring some chaining slow rain and no lightning. The last thing we need right now is a natural fire starter.
Member Since: June 12, 2005 Posts: 6 Comments: 8186
Quoting HTV:

Please do as I do....Think Fish Storms!


Actually don't, with this drought think slow moving TS
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425
Surgeon General warns not to stare at the graphic too long for your eyes may be permanently damaged. That is one busy item.

I feel just fine however.

Member Since: June 12, 2005 Posts: 6 Comments: 8186
Quoting RitaEvac:
Florida drought, TX drought, maybe the 2 states that get hit by the big ones this year...


Around here those are fighting words. LMAO J/K
Member Since: August 12, 2007 Posts: 2 Comments: 2838
426. HTV
Quoting RitaEvac:
Florida drought, TX drought, maybe the 2 states that get hit by the big ones this year...

Please do as I do....Think Fish Storms!
Afternoon....

Based on this map of Dynamical/Statistical models my guess is la nina could very well hang on a tad longer then currently forcasted and go neutral for the heart of the season. Adrian

Member Since: May 14, 2006 Posts: 8 Comments: 13807
423.

Niiice
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Quoting NEwxguy:
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.


Was that your bright white shivering reflection we saw on the sat pic last week? :)

§
Member Since: June 12, 2005 Posts: 6 Comments: 8186
75 days till Hurricane season.
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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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