Severe storms possible for southern Ontario, including Toronto / US: storms kill seven in the South and Midwest as forecasters warn of catastrophic rains and floods / Days of severe storms leave 18 dead as rising rivers threaten US south and midwest / Why some storms brew up to extreme dimensions in the middle of America--and why it's happening more often / Severe storms in the Midwest and South kill at least 20 people / What to know about the severe storms and flash flooding hitting parts of the U.S. / What to know about the severe storms and flash flooding hitting parts of the US / US: Severe storms claim 16 lives, including children