Horrible news out of Dallas/Fort Worth Area today, at least two tornadoes slammed into areas south of Dallas Tuesday afternoon, causing widespread damage, NBC News reported. The National Weather Service described them as "large and extremely dangerous." This footage shows big-rigs being thrown into the air and power lines exploding as a large funnel cloud advanced in a populated area. "There's tremendous damage here," said NBC 5 reporter Ken Kalthoff in Lancaster.   NBCDFW reported the Dallas/Fort Worth International Airport was hit by large hail.   American Airlines said it had cancelled all operations at the airport due to the severe weather. A tornado emergency has been issued for south Dallas County, while severe thunderstorm and a tornado watch are in effect for most of North Texas until 8 p.m. local time, thoughts and prayers are with all the families affected.