Tag: heat

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Comparison of 2012 to 1988 in Illinois

Precipitation

The first figure shows the statewide precipitation departures by month for both 1988 (blue) and 2012 (red) in Illinois, using the 1981-2010 average as normal. There are several interesting features:

  • the period from January to March was actually drier in 2012 than 1988;
  • the 1988 drought started abruptly in April with dramatically less precipitation; April 2012 was dry but less so than February or March;
  • the precipitation departures in May and June of 1988 were slightly more severe (1/2 inch drier for each month) than 2012;
  • by the end of June, the precipitation deficit was 7.83 inches in 1988 and 7.25 inches in 2012;
  • while less severe than June, precipitation continued to be below normal from July to October in 1988; real relief did not arrive until November.
    Monthly precipitation departure in Illinois for 1988 (blue) and 2012 (red). Click to enlarge.

Temperature
The next figure shows the statewide temperature departures by month for both 1988 (blue) and 2012 (red) in Illinois. There are several interesting features here as well:

  • temperatures from January to March in 2012 were much warmer than normal while they were much cooler than normal in 1988; in fact, January and February was significantly colder in 1988;
  • temperatures in April, May, and June were all above normal in 2012;
  • it wasn’t until May that temperatures in 1988 started to be warmer than normal;
  • warmer than normal temperatures continue in 1988 until October.
Monthly temperature departures in Illinois for 1988 (blue) and 2012 (red). Click to enlarge.

Summary

In summary, the 1988 drought started later than the 2012 drought, but once started it was more intense in the April-June period. However, temperatures were much warmer in 2012 than in 1988. In my opinion, those two factors balance out, making the the 1988 and 2012 very comparable at this point.
How is July unfolding? For the first 17 days of July, the precipitation amounts are identical between 1988 and 2012 at 0.8 inches (40% of normal for that period). However, temperatures for the first 17 days of July 1988 averaged 79.1 degrees, 3.3 degrees above normal. For this July, the average temperature was 82.3 degrees, 6.5 degrees above normal.

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First Half of July – Hot and Dry

Rainfall

The statewide average rainfall for Illinois in the first half of July is only 0.8 inches. That is 1.2 inches below average or 40 percent of average. The statewide 1981-2010 average rainfall for the first half of July is 2.0 inches.
The driest July on record was July 1930 with only 1.01 inches. Next in line was 1916 with 1.23 inches and 1936 with 1.24 inches. More recently, 1983 came in 12th place with 1.93 inches and 1988 came in 25th place with 2.60 inches.

Temperature

The statewide average temperature for the first half of July was 82.0 degrees, 6.2 degrees above average. The hottest July on record was 1936 at 83.1 degrees.
Based on preliminary data, there have been 186 new daily records set in July so far and another 33 tied previous records. You can check out the records yourself at http://www.ncdc.noaa.gov/extremes/records/.

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Warmest Spring on Record for Illinois

Temperature This Spring

In climatology we use the three whole months of March, April, and May as spring. It makes more sense than the astronomical definition of the March 20 – June 20. As this year demonstrates, summer-like conditions arrive long before the summer solstice. This year the statewide average temperature for spring in Illinois was 59.1 degrees. That makes it the warmest spring on record for Illinois. The statewide records go back to 1895. The five warmest springs in Illinois were:

  1. 2012 with 59.1 °F
  2. 1977 with 57.3 °F
  3. 1921 with 56.0 °F
  4. 1991 with 56.0 °F
  5. 2010 with 55.4 °F

May

The statewide average temperature for May in Illinois was 68.1 degrees. That is 5.7 degrees above normal and the 5th warmest May on record, based on preliminary data. The five warmest month of May were:

  1. 1962 with 69.5 °F
  2. 1977 with 68.9 °F
  3. 1896 with 68.8 °F
  4. 1991 with 68.5 °F
  5. 2012 with 68.1 °F

Year to date

It was the warmest January-May on record in Illinois with an average temperature of 48.8 °F. What’s interesting is that out of the top five warmest January-May periods, three have occurred in the last 15 years.

  1. 2012 with 48.8 °F
  2. 1921 with 47.3 °F
  3. 1998 with 46.3 °F
  4. 2006 with 45.8 °F
  5. 1938 with 45.6 °F

Precipitation

The statewide average precipitation for May in Illinois was 2.4 inches. That is 1.8 inches below normal and 57 percent of normal. That makes it the 21st driest May on record. The driest May was 1934 with 1.03 inches.
The statewide average precipitation for spring in Illinois was 7.71 inches. That is 3.65 inches below normal and the 18th driest spring on record. The driest spring on record was 1934 with 5.16 inches. In case you are wondering, 1988 was the eleventh driest spring at 6.87 inches.
The May 29 US Drought Monitor has several areas in Illinois in “abnormally dry” conditions and far southern Illinois in moderate drought. The good news is that significant rains fell in northwestern Illinois after the map was released so some of those abnormally dry conditions in that part of the state have been washed away.

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Sixth Warmest July on Record for Illinois

It comes as no surprise that this July was one of the warmest on record. The statewide average temperature for Illinois was 80.1 °F. That is 4.3 °F above average and the 6th warmest on record (tied with 1955). Here is how the top six Julys look:

  1. 83.1 in 1936
  2. 81.7 in 1901
  3. 81.3 in 1934
  4. 80.4 in 1916
  5. 80.2 in 1921
  6. 80.1 in 2011 and 1955

While the daytime temperatures were impressive, it was the very warm nighttime temperatures that pushed this July into the top 10 list. Here in Champaign-Urbana, we were the 7th hottest July in terms of daytime high temperatures but we were the 2nd hottest July in terms of nighttime low temperatures. Why so hot, especially at night? The high humidity levels experienced in July prevented the nighttime temperatures from cooling off.
Looking at stations with records of at least 30 years, we had 168 broken and 71 tied daily record high low temperatures. Meanwhile we had only 28 broken and 24 tied record daily high temperatures.
At least 38 sites reported temperatures reaching the 100°F mark. The hottest temperature reported for July was 105°F at Dixon Springs on July  13 and Streator on July 25.

Does this July indicate climate change?

Below is the graph of July temperatures for Illinois from 1895 to present. While July 2011 was outstanding compared to recent decades, we have had other stretches of hot Julys. In my opinion, the most interesting feature is the dramatic rise in July temperatures in the 1920s and first half of the 1930s that maximized in 1936 before returning to values closer to the long-term average.
As the shading indicates, we were more often warmer than average (red shading) in the first half of the 20th century. We were more often cooler in the second half of the 20th century and in the early 21st century. Another thing to note is that 2009 was the coldest July on record for Illinois with an average of only 70.2°F and now this year with the 6th warmest.
At this point, this July does not indicate a pattern of hotter summers in July. The large year to year variability as well as the tendency for trends of up to 10 years to appear and disappear show just how hard it is to detect long-term (i.e., multi-decade) climate change in the Illinois records for summer.

July temperature for Illinois
July Temperature, Average for Illinois from 1895 to 2011. The arrow denotes 2011. The long term averages (1895-2010) is shown as a horizontal line in the middle of the chart. Five-year moving averages are plotted in comparison to the long-term average and shaded as red (above average) or blue (below average) curves. Click to enlarge. Source: Southern Climate Impacts Planning Program.