The storms stretch from the Gulf Coast to the Midwest and were moving into the Northeast and New England Sunday, said Marc Chenard, a meteorologist with the NWS's Weather Prediction Center in College Park, Maryland.
About a foot of snow could fall Sunday on parts of northern Wisconsin, upstate Michigan and North Dakota, he said.
The threat of violent thunderstorms stretch from a corridor from the Florida peninsula to North Carolina, South Carolina and Virginia, said Chenard.
"No tornado warnings are issued yet for the area, but the conditions could be ripe for some in the afternoon," he said. On Friday, the system produced 17 reports of tornadoes in Arkansas, Louisiana, Missouri
and Texas, the weather service said. Four people were injured and 160 buildings damaged in a possible tornado in northwest Arkansas, local media reported. At least two tornadoes packing winds up to 90 miles (145 km) per hour was reported in Mississippi this weekend, the NWS said.
The weather is blamed for two traffic fatalities in western Nebraska and Wisconsin, according to National Public Radio.