Temporary closure becomes permanent because of heavy snow and avalanches.

OKANOGAN — The gates are closed until spring on the North Cascades Highway.

Tuesday morning, Nov. 20, nearly two feet of new snow and several snow slides coupled with a weather forecast calling for more through the Thanksgiving weekend prompted the Washington State Department of Transportation to make Monday’s temporary closure permanent.

Twisp Maintenance Supervisor Don Becker said “It would be unsafe for our crews and the public to be up there.”

The highway closed Monday morning when snow began falling at the rate of more than two inches per hour, causing three snow slides. “By this morning,” said Becker, “we had 19 to 20 inches of new, heavy, wet snow bringing the totals on the shoulders to 38 to 42 inches. That’s above the 2-1/2 to 3 feet accumulation that fills up the avalanche chutes. We found slides below three of the Liberty Bell avalanche chutes; the largest was 14 feet deep and 50 feet wide. We found more, smaller slides in the Cutthroat Ridge zone, but at the lower elevations, it was the rain that caused the problems, dumping mud, rocks and trees across the road.”

Last year, the highway closed temporarily on Nov. 15 and for the season on Nov. 21. The 37-mile winter closure zone begins seven miles east of Diablo Dam at milepost 134 on the west side of Rainy Pass (elevation 4,855 feet) to nine miles west of Mazama at milepost 171 below Washington Pass (elevation 5,477 feet). Businesses in all towns and communities west of milepost 134–Newhalem, Marblemount, Rockport, Concrete, Hamilton, and Lyman–are reachable and open for business.

Last spring, the highway reopened May 10. SR 20 typically reopens between the last week in March and the first week in May. The earliest opening was March 10, 2005. In 1976, a drought year, it remained open all winter.

For more information, go to the North Cascades Web page (www.wsdot.wa.gov/traffic/passes/northcascades) and the North Cascades Flickr photo site: www.flickr.com/photos/wsdot/sets/72157626170712679/.

posted 11.20.12, 11:55 a.m.