State-by-State and Regional Analysis of Temperature and Precipitation Trends

By: Christopher C. Burt , 7:30 PM GMT on April 07, 2012

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State-by-State and Regional Analysis of Temperature and Precipitation Trends 1895-2011

I’ve been pouring over the statistical database that the NCDC maintains on temperature and precipitation trends and pulled together a brief state-by-state analysis. The database begins in 1895 (when the U.S. Weather Bureau began to homogenize its observation techniques) and is current up to February 2012. There are some surprises, but by and large the trend is certainly towards warmer and wetter conditions in most regions of the country.

Here is what the trends have been for each state (excluding Alaska and Hawaii). The complete analysis can be found here.

I’ve noted the overall trend for each state after the statistics and highlighted in bold the cases where the trend change has been significant; meaning a change in temperature greater than 1.0°F (up or down) or a change in precipitation greater than 5% (dryer or wetter) over the long-term mean. The percentage is change in precipitation over the past 116 years relative to the state’s long-term average:








The Case of Texas

Although last year was the 2nd warmest and 2nd driest year on record for the state of Texas, the long-term trend shows little change in either temperature or precipitation over the past 116 years for America’s largest state (ex-Alaska), one of the few states to experience such (others include North Carolina, Oregon, Florida, and Georgia).



There has been a spike of warmer than normal temperatures in Texas since 2000 but over the long-term this has been mitigated by a long period of cooler than normal temperatures between 1958-1997.



Extreme variability seems to by the ‘normal’ for Texas precipitation on a year-on-year basis, so in spite of last year’s record drought, the overall trend shows little change.

Some Conclusions

TEMPERATURE

Only six states have experienced a cooling trend (but none ‘significant’—cooler by 1°F or more). The states showing the greatest cooling trend are Alabama (-0.7°F), Georgia (-0.6°F), and Mississippi (-0.6°F). Forty states have experienced a warming trend (with 20 showing a significant 1°F or more increase in temperature. The states showing the greatest increase in temperature are North Dakota (+2.6°F), Nevada (+2.4°F), and Rhode Island (+2.4°F). Three states have shown no change: Texas, Maine, and West Virginia.



My crude attempt at mapping the temperature trends (I’m not a cartographer or Photoshop wiz, sorry!). The deep red indicates states that have seen a +1.0°F or more increase in temperature above the 116-year mean. The orange states have seen a minor warming (+0.1°-0.9°F) and the blue states have seen a decrease in temperature over the long-term mean. Maine, Texas and West Virginia showed no change in their temperature trends.

PRECIPITATION

Forty-one (41) states have trended wetter with 34 of these ‘significantly’ wetter (a change of more than 5% over the long-term mean). The greatest increase has been in Massachusetts where an amazing increase of 29.2% has occurred over the past 116 years. The other states showing the greatest increase in precipitation are Rhode Island (+28.3%), South Dakota (+25.7%), and Connecticut (+24.6%). Only 7 states have seen a drying trend and only 2 of those ‘significantly’ so (by more than 5%). The states showing the greatest drying trend are Wyoming (-8.5%), California (-7.7%), and Maine (-4.8%). The Maine figure is especially interesting since every other New England state has seen a significant increase in precipitation. Indeed, the Northeast region as a whole has seen a +12.4% increase in precipitation from the long-term average. The South Dakota trend seems strangely anomalous relative to its surrounding states. South Dakota has relatively few weather stations (COOP or otherwise) that may be a clue to the anomaly. Strange nonetheless (see more about this towards end of blog).



Another crude map illustrating the precipitation trends. The blue states represent where a ‘significant’ increase of 5% or more has occurred. The orange states have seen a decrease, but only California and Wyoming have seen a ‘significant’ decrease of 5% or more. The ‘white’ states have seen either no change or an insignificant change of less than +5% in their respective precipitation trend. Again, these are figures representing percentage change above or below the 116-year average.

Trends by Region

Here is the NCDC official map outlining their regional designations:



All the climatological regions have seen their temperatures increase except for the Southeast that has seen a slight cooling trend (-0.1°F). The Northern Rockies and Plains have seen the greatest temperature increase (+1.5°F), closely followed by the West and Southwest (both +1.4°F). All regions except the West have seen a trend towards wetter conditions with the Northeast leading the way (+12.4%), followed by the Upper Midwest (+10.7%). The West has trended drier by -4.2%.

Here is how the data breaks down by regions:



You can look at more detailed data for your specific location within a state by looking at this map:



Here is a map of all the U.S. Climatological Divisions.

You can see the data or each division by following the link here. This link, for instance, shows the trend for eastern Massachusetts (division 3 in the state). You can look at each and every year’s average annual precipitation for the division on the bar graph under the chart. Below is the precipitation trend for climate division 6 in South Dakota (central part of the state) where the increase has been 35.7%. This is the most anomalous of any division in the U.S. I have yet identified.






For the entire contiguous U.S. the temperature trend has been +1.2°F and +6.1% wetter compared to the mean over the 116 years since 1895.


Christopher C. Burt

Weather Historian

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7. Christopher C. Burt , Weather Historian
6:23 AM GMT on April 09, 2012
Sorry, but for some reason the URL will not copy and paste as I thought. So you'll have to do your own homework to see this. Just click on the link in my blog (last word 'here' in 2nd paragraph), then choose 'March 2011' as the date and then -single month' as the time frame.

Quoting BobCarver:
It's somewhat misleading to observe the mean temperature for all years because you could have a situation where summers are getting warmer and winters getting cooler while the mean stays the same. Clearly, there would be a trend which would be smeared out by averaging. It's much more enlightening to look at seasonal groupings, such as spring, summer, fall and winter, when looking for long term trends in temperature. In fact, if you do this for Texas, you'll see a definite pattern of warming during the summer months. Thanks for introducing us to this wonderful tool, Burt!
Member Since: February 15, 2006 Posts: 316 Comments: 296
6. Christopher C. Burt , Weather Historian
6:17 AM GMT on April 09, 2012
Sorry, that URL didn't work (to see the USA March-single month data). Try this :

http://www.ncdc.noaa.gov/temp-and-precip/time-ser ies/index.php?parameter=tmp&month=3&year=2011&filt er=1&state=110&div=0

Quoting BobCarver:
It's somewhat misleading to observe the mean temperature for all years because you could have a situation where summers are getting warmer and winters getting cooler while the mean stays the same. Clearly, there would be a trend which would be smeared out by averaging. It's much more enlightening to look at seasonal groupings, such as spring, summer, fall and winter, when looking for long term trends in temperature. In fact, if you do this for Texas, you'll see a definite pattern of warming during the summer months. Thanks for introducing us to this wonderful tool, Burt!
Member Since: February 15, 2006 Posts: 316 Comments: 296
5. Christopher C. Burt , Weather Historian
6:13 AM GMT on April 09, 2012
This is a great tool. Let's see how March 2012 stands up to the current hottest March on record, that of 1910 (we should know the results this coming week sometime):

http://www.ncdc.noaa.gov/temp-and-precip/time-ser ies/index.php?parameter=tmp&month=3&year=2011&filt er=1&state=110&div=0

Copy and paste the above URL for USA March (single month) records.





Quoting BobCarver:
It's somewhat misleading to observe the mean temperature for all years because you could have a situation where summers are getting warmer and winters getting cooler while the mean stays the same. Clearly, there would be a trend which would be smeared out by averaging. It's much more enlightening to look at seasonal groupings, such as spring, summer, fall and winter, when looking for long term trends in temperature. In fact, if you do this for Texas, you'll see a definite pattern of warming during the summer months. Thanks for introducing us to this wonderful tool, Burt!
Member Since: February 15, 2006 Posts: 316 Comments: 296
4. BobCarver
4:55 AM GMT on April 09, 2012
It's somewhat misleading to observe the mean temperature for all years because you could have a situation where summers are getting warmer and winters getting cooler while the mean stays the same. Clearly, there would be a trend which would be smeared out by averaging. It's much more enlightening to look at seasonal groupings, such as spring, summer, fall and winter, when looking for long term trends in temperature. In fact, if you do this for Texas, you'll see a definite pattern of warming during the summer months. Thanks for introducing us to this wonderful tool, Burt!
Member Since: May 18, 2010 Posts: 0 Comments: 3
3. Christopher C. Burt , Weather Historian
11:49 PM GMT on April 08, 2012
Actually, +1.2°F is quite significant. Remember that this is an increase over the mean for ALL 116 years, so the mean has risen as well thanks to how warm the past 14 years have been. If you look at the first link I provided (at the end of the 2nd paragraph of my blog), you'll see how the temperature really warmed since 1997. If one took the average for EACH decade since 1895 you would see that the recent warming was considerably greater during the past decade compared to earlier decades. The 1960s and 1970s were really cool, so that also skews the overall change (trend) when taking the entire POR in to account.

You raise a very interesting question about whether or not there has been an increase in reporting sites over time. I've always wanted to know, for instance, how many different observation sites there have been on a year-to-year basis since 1895. I have never been able to find figures about that (the number of observation sites over time).


Quoting Soap2:
Seriously?? In 120 years the climate has only warmed up by 1 degree Fahrenheit? When I look at city level data it seems so much higher. Is it possible this trend is caused by the addition of more weather stations in cooler, rural areas in most states?
Member Since: February 15, 2006 Posts: 316 Comments: 296
2. Soap2
7:18 PM GMT on April 08, 2012
Seriously?? In 120 years the climate has only warmed up by 1 degree Fahrenheit? When I look at city level data it seems so much higher. Is it possible this trend is caused by the addition of more weather stations in cooler, rural areas in most states?
Member Since: November 21, 2011 Posts: 0 Comments: 11
1. rgibbs3885
5:51 PM GMT on April 08, 2012
awesome article!
luv reading ALL the wunderground contributors!
Member Since: September 22, 2004 Posts: 0 Comments: 7

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About weatherhistorian

Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.