What happened to summer?
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[AUG. 16, 2004]
overall temperature for summer 2004 is averaging 2.7 degrees below
normal through Aug. 12, with record-breaking lows. If this
continues, it will be the fourth coldest summer and the second
coldest August in Illinois since 1900. Not only are the temperatures
colder than average, but there just hasn't been much hot weather
this summer," says Jim Angel, state
climatologist with the
Illinois State Water Survey, a
division of the Illinois Department of Natural Resources.
"This is due to a summer-long weather
pattern dominated by cooler, drier Canadian air rather than warmer,
more humid Gulf of Mexico air. Statewide, summer temperatures were
below normal by 1.9 degrees in June, 2.9 degrees in July and by 5
degrees for the first two weeks of August," says Angel.
An evolving feature of the nation's
weather patterns over the last century has been a northward shift of
the jet stream, producing warmer temperatures over the western
United States, and a southward dip in the jet stream, producing
cooler temperatures over the Midwest and the East.
The summer of 1915 was the coldest on
record, with temperatures averaging 3.9 degrees below normal. More
recently, the summer of 1992 was almost as cold, with temperatures
averaging 3.4 degrees below normal due to the lingering effects of
the Mount Pinatubo eruption in the Philippines in 1991.
The hottest temperatures reported this
summer are averaging 93 degrees statewide, down from the normal 97
degrees. Highs at or above 95 degrees have occurred on only one to
three days in the southern half of Illinois and none in the northern
half instead of the usual two to six such days at most Illinois
locations by now. Temperatures at or above 90 degrees also have been
noticeably less frequent: two to four days rather than 10 to 16 days
in northern Illinois, four to eight days rather than 16 to 24 days
in central Illinois and eight to 14 days rather than 24 to 26 days
in southern Illinois.
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Statewide, summer rainfall is averaging
8.84 inches, 94 percent of normal, and year-to-date precipitation is
averaging 24.58 inches, exactly normal, through Aug. 12.
The National Weather Service is calling
for colder-than-normal temperatures for the next two weeks. "By
then, we will be pretty much through August, and the likelihood of
really hot weather will diminish rapidly," says Angel.
"Historically, the type of summer we're having this year does not
necessarily foreshadow a colder-than-normal winter. In fact, it
often has led to near-normal winters," concludes Angel.
State Water Survey news release]