YELLOWSTONE NATIONAL PARK - Visitors to Yellowstone National Park this week are encountering snow that has forced temporary road closures.

The National Weather Service said between 6 and 12 inches of new snow was possible along Sylvan Pass on the road between the east entrance and Fishing Bridge. Seven inches had fallen by Thursday morning at Sylvan Lake.

Many park roads above 8,000 feet elevation were slick, and park visitors were urged to check with the National Park Service on road conditions.

The Weather Service issued a snow advisory Thursday for northwest Wyoming, including Yellowstone, and for the mountains in north-central Wyoming. Up to 20 inches of snow was possible in some higher elevations.

The weather was expected to improve in northwest Wyoming by this weekend.