At least 50 million people in seven states were at risk Thursday of tornadoes, large hail or wind damage in what forecasters said was expected to be the first significant tornado outbreak of the season, NBC News reported. The Mississippi and Ohio Valleys are entering the most dangerous part of the year for tornadoes. The cities under threat included Little Rock, Ark.; Memphis, Tenn.; and Joplin, Mo., which was all but leveled by a tornado that killed 161 people three years ago. The storm system is expected to move east on Friday, threatening parts of the Mid-Atlantic and Southeast.