In Chicago, 1921 keeps 'hottest' title

Chicago logged its 10th warmest year in 2006 with an average temperature of 52 degrees, according to the National Weather Service in Romeoville.

The warmest year on record came in 1921, when the average temperature was 54.5. The normal average temperature is 49.1 degrees, said Charles Mott, a weather service meteorologist.

The slightly higher-than-average temperatures can be attributed to the fact that it was an El Nino year, which meant the jet stream carried warmer air across the country, Mott said.

"The flow coming in from the Pacific Ocean" means "all of the moisture gets dropped out west because of the Rocky Mountains and then on our side of the Rocky Mountains is the warm and dry side," Mott said. He said it was uncertain whether greenhouse gases had an effect on the temperatures.

During the past decade, the average annual temperatures have hovered around the 50-degree mark, but each of the past four years has registered a slight but steady increase from 48.9 degrees in 2003 to 52 degrees in 2006.

For this weekend, Chicago area residents should see a return to normal winter conditions, Mott said.

On Saturday and Sunday, temperatures will reach the mid- to high 20s, but the lows will fall into the teens.

That will mark the coldest days yet this winter, Mott said. And there's still a few months to go.

ldonovan@suntimes.com