Visit msnbc.com for breaking news, world news, and news about the economy Source: MSNBC Oklahoma City — The heat was on Monday for millions of Americans from the Upper Midwest to Texas and Oklahoma, where roads buckled and poultry farmers deployed fans and watered rooftops to protect flocks. The National Weather Service put 18 states stretching from North Dakota to Texas and East to Ohio under a heat warning, watch or advisory. It said as many 13 deaths in the past week [...]