Friday, Sept. 3

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Not your typical
long, hot summer    
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[SEPT. 3, 2004]  "If you think that the weather in Illinois this summer has been cool and wet, you're right; but these conditions are not unique to Illinois," said Jim Angel, state climatologist. "Temperatures this summer in most of the eastern two-thirds of the United States also have been cooler than normal, as frequent intrusions of Canadian air have dominated the region. By contrast, warmer than normal temperatures have affected the northwestern United States."

Angel is associated with the Illinois State Water Survey, a division of the Illinois Department of Natural Resources

"While the magnitude of the cool temperatures this year has been extraordinary, the pattern is not unique to 2004," he said. "Following a period of frequently very hot summers in the 1930s and early 1950s, the period since the late 1950s has seen relatively cool summers on average in Illinois, with no trend over that period. At the same time, summers in the western United States have become progressively hotter.

"This regional difference in trends is probably caused in large part by a change in the overall atmospheric circulation patterns. The ultimate causes of these shifts are not clear at this time.

"Temperatures in Illinois this summer are averaging 3.1 degrees below normal statewide, with even colder August temperatures, 4.9 degrees below normal. Both summer and August rank as the fifth coldest since 1895. In recent years, only 1992 was ranked colder -- [the] third coldest summer and August since 1895. The 1915 record still stands for the coldest summer, 3.9 degrees below normal, and coldest August, 5.8 degrees below normal."

 

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Temperatures this August are averaging 68.7 degrees, with precipitation averaging 5.45 inches, 149 percent of normal. Temperature extremes this month have ranged from 40 degrees at Congerville on Aug. 15 to 97 degrees at Kaskaskia on Aug. 19. Grayville reported the largest one-day precipitation total: 6.87 inches on Aug. 26.

"June-August temperatures are averaging only 70.7 degrees, and precipitation is averaging 12.87 inches, 111 percent of normal," Angel said.

Although the National Weather Service is calling for an increased chance of cooler than normal temperatures for September, the temperature outlook for November-January is neutral, suggesting a return to more seasonable temperatures.       

"The type of summer we're having this year does not necessarily foreshadow an early frost," Angel said. "For example, an analysis of the 10 coldest summers in Champaign-Urbana yields a first fall frost date only six days earlier than the 1971-2000 average of Oct. 17. The first frost typically occurs on Oct. 7-14 (northern Illinois) and Oct. 1421 (central and southern Illinois)."

[News release from Eva Kingston, editor,
Illinois State Water Survey]

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