- NEW: Parts of seven states in path of storm
- Intense tornadoes are possible, forecasters say
- Football game officials in Chicago warn fans to listen for evacuation announcements
- Other states likely to see winds of at least 31 mph
(CNN) -- Chicago and other areas of the Midwest could see some dangerous weather Sunday, with parts of seven states under a tornado watch, according to the National Weather Service.
One fast-moving tornado had already touched down near Washington, Illinois, a few miles east of Peoria, the weather service said. It was moving northeast at 55 mph.
Watches were in effect for parts of Illinois, Indiana, Iowa, Michigan, Missouri, Ohio and Wisconsin. Other Midwestern states are facing a wind advisory.
Forecasters said there was a possibility of intense tornadoes, large hail up to 2 inches in diameter, and damaging wind gusts -- some of them greater than 80 mph in and near the watch areas.
The watch area includes Detroit, Indianapolis and the greater Chicago metropolitan area. The storm could affect the NFL game at noon (1 p.m. ET) between the Bears and the visiting Baltimore Ravens.
Stronger than normal winds were already blowing at Soldier Field ahead of the main brunt of the storm. Flags, temporary signs and tents outside the stadium have been removed, CNN affiliate WLSreported.
"It's important that people listen to the messages today and if (they) hear a call that we want people to evacuate the stands, even though you may see play continue on the field, it's time to move to safe areas," said Soldier Field general manager Tim LeFevour.
This is a particularly dangerous situation, the National Weather Service said in a bulletin released Sunday morning.
And a tweet from the weather service in northern Indiana was even more ominous: "The worst decision you could make today is to ignore a severe/tornado warning. These storms will be nasty."
A tornado watch means that weather conditions exist that can produce tornadoes and severe thunderstorms. Conditions are favorable for long-tracked, significant tornadoes across this watch area, the Storm Prediction Center said.
A wind advisory means sustained winds of 31 to 39 mph or gusts of 46 to 57 mph are expected, the weather service said.