By Lindsay Morris TULSA, Oklahoma (Reuters) - A huge tornado touched down on Monday near Oklahoma City, and the National Weather Service urged residents to immediately take cover as a massive storm system in the middle of the country threatened to pummel as many as 10 states. "The tornado on the ground right now is huge and has hit through populated areas," Oklahoma Governor Mary Fallin said on CNN. She said it was too early to know the extent of the damage, but live television showed extensive destruction in the area. ...