NEW : A tornado touches down in Cass County , Nebraska . Missouri governor declares state of emergency after town is hit by EF-2 tornado . Risk of more tornadoes , severe weather across Central plains region . Winter storm warnings and watches issued for parts of the state .
NEW : A tornado touches down in Clay County , Nebraska . Missouri governor declares state of emergency after town is hit by EF-2 tornado . Risk of more tornadoes , severe storms across Central plains Sunday . Winter storm warnings and advisories issued for parts of the Rockies .