AUSTIN, Texas (AP) — Officials say a frigid blast of winter weather across the U.S. is likely to blame for the deaths of two people in Texas. Temperatures dropped into the single digits. Snow shut down air travel and grocery stores. More than four million people in Texas were without power Monday evening. The storm was part of a massive system that brought snow, sleet and freezing rain to the southern Plains and was spreading across the Ohio Valley and to the Northeast. The Southwest Power Pool, a group of utilities across 14 states, called for rolling outages because the supply of reserve energy had been exhausted. The governors of Texas, Oklahoma and Arkansas activated National Guard units to assist with tasks including rescuing stranded drivers.