A storm system that’s brought rain, ice and snow to the Midwest and Great Plains was blamed for fatal crashes in three states, including an accident that left four people dead in Nebraska.

The storm system stretched from Texas, where National Weather Service officials say three tornadoes hit, to the Great Lakes states and forced some schools to close. The weather service issued winter weather advisories for parts of Oklahoma, Kansas, North Dakota, Missouri, Iowa, Minnesota and Wisconsin. Flood warnings were in effect in Illinois, Indiana and Michigan with flood watches in Texas and Arkansas.

Weather service officials urged motorists not to drive onto flooded roadways and to find alternate routes.