The National Weather Service issued a winter weather advisory for most of Southwest Colorado on Thursday, effective until 9 a.m. Friday.

In Cortez, light snow began to fall about 10 a.m. Thursday. The storm was expected to drop 4 to 8 inches of snow, with highest amount in the mountains and produce patchy fog.

The advisory included the areas of Silverton, Hesperus, Rico, Ouray, Telluride and Lake City. Drivers should expect slippery roads, especially over Lizard Head, Red Mountain, Coal Bank and Molas passes.

On Thursday morning, a commercial vehicle chain law was issued for Coal Bank and Molas passes north of Durango. All commercial vehicles are required to have chains or alternative traction devices. All passenger vehicles must have snow or mud/snow tires, use chains or alternative traction devices or have a four-wheel/all-terrain vehicle.

In Montezuma and Dolores counties, there is a 60-70 percent chance of snowfall on Thursday. Less than a half-inch of snow was expected during the day, and up to 2 inches overnight. On Friday, there’s a 40 percent chance of snow, and a 20 percent chance overnight. Daytime high temperatures were expected to reach 35 degrees, then drop to the mid-20s overnight.

Skies are expected to begin clearing on Saturday, and become sunny Sunday through Wednesday. Highs were expected to be in the mid- and upper 30s, and overnight lows were expected to be about 20.