Noem on Thursday added two more counties to the closure list, shuttering 54 of South Dakota’s 66 counties. Only essential personnel were told to report to work in those counties. Heavy snow and high winds are making travel dangerous.

As much as 18 inches of snow has fallen in parts of South Dakota, including Dupree and Mud Butte. The storm canceled schools, including those in Rapid City, circuit courts and the Mount Rushmore National Memorial.

The storm system knocked out power to thousands of homes and businesses in South Dakota Wednesday, disrupted air and ground travel from Colorado to Minnesota and threatened to swell rivers in the Midwest that flooded last month.