What happened to summer?    

[AUG. 16, 2004]  ^"The 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. 

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.

[Illinois State Water Survey news release]