CHAMPAIGN — July is supposed to be the hottest month of the year in central Illinois.
Not this year.
The average temperature so far this month in Champaign is 70.4 degrees, or almost 5 degrees below the historical average of 75. It's also lower than last month's average temperature in Champaign-Urbana — 73.4 degrees.
In fact, said state climatologist Jim Angel of the Illinois State Water Survey, we may be headed for the third-coolest July on record. Local weather records date to 1889.
"Number 1 on the list is 2009 at 70 degrees, and Number 2 is 1891 at 70.3 degrees," Angel said. "I don't know if we will beat Number 1 or Number 2. It will be close."
After a warmup this weekend — with predicted highs of 88 Saturday and 84 Sunday — high temperatures are expected to fall back into the 70s with lows in the 50s through at least Wednesday, according to the National Weather Service.
The average high in Champaign-Urbana at this time of the year — traditionally the peak of summer heat — is 85. The average low: 65.
The highest reading this month was 87 degrees on July 7 and 22. The lowest was 53 on July 15, 16 and 17. There have been 13 days with lows in the 50s.
The cool July weather is all because of an unusual position of the upper-air jet stream, said National Weather Service meteorologist Dan Smith in Lincoln.
Normally the jet stream runs west to east across southern Canada, but not this year.
"As you get to the north and northwest of the Great Lakes, it's fairly cool as a result of that big upper low that's up across Hudson Bay and is going to sit here for a while," Smith said. "What that actually does is to bring the flow down from the northwest to the southeast so it kinda winds around that and brings it into the Great Lakes region.
"It's holding firm, just like that big upper high last year that gave us the hot weather and never moved. This one is very stubborn and for one or two days it moves off to the northeast and brings warmer weather in. But then it just settles back south to Hudson Bay and as a result our flow is right out of Canada."
But the heat can always return late in the summer, Angel noted.
"I can remember how cool July 2009 was — we finally got summer weather in August and early September," he said.
The average high temperature in July 2009 was 79.2 degrees. A month later, the average high was 80.5. There were no 90-degree days in July but three in August.
"In a typical July, we have long stretches of warm, humid weather with a day or two of cool, dry Canadian air thrown in the mix," Angel said. "This year has been the opposite, with the cool, dry air dominating — just like in 2009."
Another weather oddity: Two years ago, Champaign-Urbana lived through its second-hottest July ever with an average temperature of 82.2, including seven days with temperatures of 100 or greater and 27 days with temperatures of 90 or greater.