BIRMINGHAM, Alabama (Reuters) - At least 17 people were killed after a string of violent storms and tornadoes swept the southern United States over two days, including seven in Alabama on Friday, officials said on Saturday. All the Alabama deaths were in the southern part of the state and were caused when mobile homes were blown off their foundations, according to Alabama Emergency Management spokeswoman Yasamie Richardson August. They included an elderly man in Marengo County, a mother and two children in Washington County, and a father and his two adult children who lived near each other in Autauga County. A tornado-related death was also reported in Greene County, Mississippi, according to the county emergency management. The storm system is now moving into the Carolinas and southeast Virginia, according to Greg Carbin, meteorologist with the National Storm Prediction Center. "The east is under the gun for tornadoes and high winds," Carbin said. He predicted Saturday would be the third and final day for the deadly system, which began in Oklahoma late Thursday. Alabama Gov. Robert Bentley declared a state of emergency on Friday and surveyed the state with emergency management officials. Two elderly sisters were killed in Oklahoma late Thursday and seven people, including three children, were killed in Arkansas Friday, authorities said. Six of the seven fatalities in Arkansas were caused when uprooted trees smashed into houses, National Weather Service meteorologist John Robinson said. Robinson said he could not recall a time in recent memory when so many fatalities occurred because of fallen trees in Arkansas. Carbin said this type of storm system in the South was not unusual for April, as moist, spring air meets the remnants of cold winter air. "You have just the right combination of ingredients for severe weather," Carbin said. "This is a dangerous time in the southern United States." Tornado season typically runs from March to early July in the United States, moving from south to north as the year progresses. The storms kill an average of 70 people a year. Not all of the deaths from the storms would be officially counted as tornado deaths, as some were likely due to high winds, Carbin said. The worst U.S. outbreak of tornadoes on record occurred on April 3-4, 1974, when 307 people were killed by 148 twisters in 13 states. Tennessee was hit by heavy rains and damaging winds Friday, and many homes remain without power. Rainfall totals of about three inches were not unusual across the state. Storms , some severe, also were expected Saturday from the Florida Panhandle through eastern and southern Georgia, according to weather.com. Elsewhere, fire danger continues over the dry southern plains and some upper Midwestern states were hit by snow on Saturday. In the northeast, heavy rainfall was possible in Pennsylvania and upstate New York, the web site said. Weather experts are still trying to determine how many tornadoes touched down over the last few days.