Get a weather radio with SAME (Specific Area Messaging Equipment(?)) technology. Set the SAME code(s) for your home areas(s). They are not too expensive, so get several. They also make great gifts. The National Weather Service issues tornado warnings almost entirely based on doppler radar returns, which typically gives 10+ minutes of of warning. (You'll note that the warning will say something like "...doppler radar indicated a possible tornado 10 miles southwest of yourtown moving northeast at 60 miles an hour...")

JimJr