CHEYENNE, Wyo. (AP) — Snow is causing slick travel conditions over much of northern and eastern Wyoming.

A winter storm warning was posted Friday morning for areas of Niobrara, Converse, Weston, Crook and southern Campbell counties, including the cities of Glenrock, Lusk, Douglas, Sundance and Newcastle.

The cities of Cheyenne, Casper, Sheridan, Gillette and Worland were under a winter weather advisory.

Up to 18 inches (45 centimeters) of snow was possible in the Snowy and Sierra Madre ranges in south-central Wyoming.

The storm, which entered the state Thursday, dumped around 12 inches (30 centimeters) of snow in parts of northwest Wyoming by Thursday night.