Site owners

  • Timothy Folkerts

March 2012 US Temperature Records


Statistical analysis suggests that this March was exceptionally hot, and March has been unusually warm for the entire last decade.  In fact, annual temperatures have been on a warm streak for nearly 2 decades.


In March, many record high temperatures were set across the US.  So how unusual were the March temperatures?  How unusual have other months been?

"Control charts" are a standard industrial technique for detecting trends in data.  For a series of data like temperatures for a specific month, the "I Chart" chart is appropriate.  All of the standard tests available in Minitab were applied to each month's data.  These tests include:
  • TEST 1. One point more than 3.00 standard deviations from center line.
    Looking for individual outliers.

  • TEST 2. 9 points in a row on same side of center line.
    Looking for a shift in the mean.

  • TEST 3. 6 points in a row all increasing or all decreasing
    Looking for a slope.

  • TEST 4. 14 points in a row, alternating up and down
    Looking for short-term oscillations.

  • TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
         one side of CL).
    Looking for clusters that are unusually high or low.

  • TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
         one side of CL)
    Looking for clusters that are unusually high or low..

  • TEST 7. 15 points within 1 standard deviation of center line (above and below
         CL).
    Looking for decreased variability.

  • TEST 8. 8 points in a row more than 1 standard deviation from center line
         (above and below CL)
    Looking for increased variability.

 
All of the standard tests available in Minitab were applied to each month's data (and to the annual average of the monthly data).  The charts and complete results are posted below, but here are some highlights.

  • There were only 4 months that triggered Test 1.  The fact that the first two were in the first third of the years and the second two were both in the final third is, in itself, evidence of warming.
    • 1917-MAY    (cold)
    • 1925-OCT    (cold)
    • 1998-SEP     (hot)
    • 2012-MAR    (hot)

  • Test 1 was triggered three times, again supporting a warming trend.
    • 1917    (cold)
    • 1998    (hot)
    • 2006    (hot)
  • Test 2 was triggered several times, again supporting the notion of global warming over this period.  There was an unusual string of warm July's in the middle third of the years, with two addition strings of hot months in the last third.
    • 1930 - 1944 JUL     (hot streak)
    • 2003 - 2012 MAY    (hot streak)
    • 2003 - 2011 NOV    (hot streak)

            Furthermore, the annual data shows even stronger trends

  • 1901-1909      (cold streak)
  • 1911-1920      (cold streak)
  • 1964-1972      (cold streak)
  • 1993-present  (hot streak)
  • When Tests 5 & 6 for unusual clusters were triggered, it was almost universally for cold clusters early on, and hot clusters later. 



So these results point to a statistically significant
  • shift to warmer temperatures in the last decade
  • culminating in an exceptionally warm individual month.

Of course, the whole reason this year's data was studied was because it had been noted that this years was unusually warm.  This provides a clear bias, since there was a special reason to check this month's data. The data for 1910 just BARELY misses the 3 standard deviation test, so we could consider it potentially significant, although it is not part of a larger trend, so it is more clearly an individual outlier, rather than just slightly unusual within a long-term trend.


All data is from the National Oceanic and Atmospheric Administration National Climatic Data Center.



March

i
April

May

june

July

August

September

October

November

December

Annual






Test Results for I Chart of Jan

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  85

TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
     one side of CL).
Test Failed at points:  108

 
Test Results for I Chart of Feb

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  98, 106

TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
     one side of CL).
Test Failed at points:  9

 
Test Results for I Chart of Mar

TEST 1. One point more than 3.00 standard deviations from center line.
Test Failed at points:  118

TEST 2. 9 points in a row on same side of center line.
Test Failed at points:  117, 118

 
Test Results for I Chart of May

TEST 1. One point more than 3.00 standard deviations from center line.
Test Failed at points:  23

 
Test Results for I Chart of Jun

TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
     one side of CL).
Test Failed at points:  13, 14, 96

 
Test Results for I Chart of Jul

TEST 2. 9 points in a row on same side of center line.
Test Failed at points:  44, 45, 46, 47, 48, 49

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  42

TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
     one side of CL).
Test Failed at points:  11, 12, 13, 15, 40, 41, 42, 112, 113

 
Test Results for I Chart of Aug

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  43, 109

TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
     one side of CL).
Test Failed at points:  17, 18, 44, 74, 113

 
Test Results for I Chart of Sep

TEST 1. One point more than 3.00 standard deviations from center line.
Test Failed at points:  104

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  39

 
Test Results for I Chart of Oct

TEST 1. One point more than 3.00 standard deviations from center line.
Test Failed at points:  31

TEST 7. 15 points within 1 standard deviation of center line (above and below
     CL).
Test Failed at points:  97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107

 
Test Results for I Chart of Nov

TEST 2. 9 points in a row on same side of center line.
Test Failed at points:  117

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  107

 
Test Results for I Chart of ANNUAL

TEST 1. One point more than 3.00 standard deviations from center line.
Test Failed at points:  23, 104, 112

TEST 2. 9 points in a row on same side of center line.
Test Failed at points:  15, 25, 26, 78, 111, 112, 113, 114, 115, 116, 117

TEST 5. 2 out of 3 points more than 2 standard deviations from center line (on
     one side of CL).
Test Failed at points:  105, 107, 112, 113

TEST 6. 4 out of 5 points more than 1 standard deviation from center line (on
     one side of CL).
Test Failed at points:  107, 108, 109, 110, 111, 112, 113

TEST 8. 8 points in a row more than 1 standard deviation from center line
     (above and below CL).
Test Failed at points:  111, 112, 113

* WARNING * If graph is updated with new data, the results above may no
          * longer be correct.



Comments