Students might have welcomed the relief from the hot sun and coolness the clouds brought early Tuesday afternoon, but the threat of a tornado drowned sighs of relief.

The Rockford Weather Service issued a tornado warning at about 2 p.m. after a tornado was spotted in the Pecatonica-Byron area—about 40 to 45 miles west of DeKalb.

A spokeswoman for the DeKalb Municipal Airport also said a tornado was spotted in the Rockford area.

The sky turned black over NIU at about 2:30 p.m. At about 2:45 p.m., heavy rains and hail hit, making it hard for students to get to and from classes.

But stormy weather ended abruptly within the hour.

There is a difference between a tornado watch and a tornado warning, said NIU weather service director Dan Watt.

A tornado watch occurs when weather conditions are favorable for a tornado to occur, whereas a warning means a tornado has been spotted, Watt said.

“Your life may depend of how quickly you respond to the tornado,” he said.

People should always avoid cars, Watt said, but if they are in cars they should immediately get into a ditch and take cover.

“Persons (in buildings) should immediately take cover in a basement,” Watt said.

Meteorology Professor Allen Staver said the hot and humid weather coupled with the cool air that rolled in produced good conditions for the storms that hit Northern Illinois.

Staver said the the strongest storms, such as tornados, will bring rain. The normal lifetime of a tornado is usually not longer than 15 minutes, but some occasionally last an hour or so, he added.

However, Staver said the odds were not likely a tornado would hit the DeKalb area.

NIU meteorologist Brendon Larson, who said Monday there would be no tornados with the cool weather that was to hit DeKalb Thursday, offered a formal apology to NIU students and said what happened in DeKalb was a macroburst, not a tornado.

A macroburst can cover an area of miles in size.

When the rain came down horizontally the macroburst stormed through DeKalb, Larson.

A macroburst occurs when there is a down draft of wind and rain which produces high winds, heavy rain and hail.

“Even with the greatest technology (meteorologists) can’t always predict storms.”