That's what the WGN Weather Blog calls the circle around a dome of hot air stretching from Texas to the Atlantic:
Yesterday this combination brought the second heavy squall line across Chicago that pinned me down at my client offices. The one last Friday had 75 km/h winds that punched out windows at Willis Tower, a few blocks away. Last night's encouraged the city to turn on the civil defense sirens:
The National Weather Service said funnel clouds were spotted in the leading edge of the storms, but there have so far been no confirmed reports of tornado touchdowns. ... Chicago's Office of Emergency Management and Communications activated emergency storm warning sirens at about 6:15 p.m. after a funnel cloud was spotted in the south suburbs, said Will Knight, a spokesman for the agency. Sirens could heard in various parts of the city, including the Loop.
Back when I grew up, the monthly siren tests (first Tuesday of the month at 10am) were tornado drills from February to October. We'd all line up along the wall and cover our heads until the sirens stopped. They still creep me out a little.
Today promises milder temperatures and winds out of the north—a typical cold-front passage. By Sunday, though, temperatures here will creep back into the 30s C and bring more storms.