At least two brief tornadoes touched down in the Chicago suburbs Monday — one in Joliet and another on the far north side of Naperville. A third tornado has also been confirmed in east central Illinois by the National Weather Service.

Meanwhile, two others were spotted just outside of Champaign, forcing many to take shelter.

Paul Sirvatka, professor of meteorology at College of DuPage, says they’re referred to as “cold season” tornadoes, where the sun isn’t a big player.

“When you have a cold season tornado in the winter months, any time you get that warm moist air, we always have a chance for tornadoes because it usually is associated with very strong winds so it is a dynamic system as opposed to one that may come from heating from the sun,” Sirvatka said. “So the winds were very strong at all levels of the atmosphere and when you have some sustained storms, you can spin up a brief albeit weak tornado.”

So far, there haven’t been large reports of significant damage in DuPage and Will counties.

So how common are tornadoes in the winter months?

Usually, tornadoes are expected in the spring, but when you get warm air at low levels and cold air higher up, that leads to a condition known as “instability.”  

“It was kind of a surprise this morning,” Sirvatka said. “They formed pretty rapidly for a short period of time. The atmosphere was just perfect — a little bit of warm moist air nosed in out of the south, coming up from Central Illinois and that little area with a lot of vertical windshield is really what led to some brief tornadoes.”

Sirvatka was among those who had to take shelter this morning at College of DuPage.

“It was right after one of my classes when someone said there was a tornado warning … While everybody else was running to seek shelter, I’m of course running outside to observe what was going on …there was some rapid vertical motion, sort of the precursor to tornadoes, right over the college,” he said. “Once that moved to the north, we gave the all clear and it quickly dissipated.”

(3/3) One other brief tornado has been confirmed per photo and video evidence in southeast Ford County near the small town of Clarence in east central Illinois. This did not produce any damage according to Emergency Management and eyewitnesses. #ILwx pic.twitter.com/T6NRVizSh3

— NWS Chicago (@NWSChicago) February 28, 2023

According to a preliminary report from the National Weather Service, the Joliet tornado reached peak winds of 85 miles per hour, was on the ground for slightly less than a mile, and caused damage to trees, fences and minor shingle damage to a handful of homes. 

The Naperville tornado touched down near Naperville North High School and cut a 1.4-mile path, reaching top winds of 80 miles per hour. 

Weather service staff are continuing to conduct investigations into other areas of possible tornado sightings or damage.

This article originally published Feb. 27 and has been updated.