The possibility continues for skiers or riders to trigger slab avalanches at the mid and high elevations. Although weak persistent layers near the base of the snowpack have become less sensitive due to lack of recent snowfall, they could still fail on some steep slopes. Conservative terrain choices are the safest way to manage this situation involving persistent slabs where the determination of which slopes remain unstable is very difficult. Avalanches are unlikely at the low elevations.
Above 8000 feet, persistent slab avalanches could be human triggered with depths of up to 4 feet deep. These slabs are most likely to be triggered on northwest through northeast aspects and by larger triggers such as snowmachines or groups of people. Previous tracks on a slope may not be an indication of stability.
The National Weather Service has issued a winter storm warning for the area, effective at 11pm tonight and continuing through 5am Thursday. The storm is to provide light accumulations through this evening before increasing in intensity as the new year arrives. By morning, approximately six more inches of snow is expected in higher terrain. The heaviest snow is expected Wednesday morning, continuing through the afternoon. Total snowfall amounts could reach twenty inches by Wednesday evening when snowfall will start to diminish. Temperatures at 9000 feet on New Year’s Day are to start in the low teens and rise into the low twenties. West winds are to be strong, particularly during the heavy snowfall and particularly in the southern forecast area. Expect averages on the summits to be between twenty and thirty-five miles per hour with higher gusts. The general avalanche hazard above 7500 feet is expected to be Considerable tomorrow morning and could be High by the afternoon. There will be two avalanche problem types. The first will involve the new snow. Given the rapid snowfall rates and strong winds expected, wind slabs will quickly form on leeward slopes. These slabs are forming upon faceted snow and crusts. They will be sensitive in the morning and will increase in both size and sensitivity as the day progresses. The other problem type involves the weak basal snow. Failure of this layer can result in large avalanches. Avalanches involving this layer will become more likely as the snowpack is loaded by the new snow and could be triggered by backcountry travelers or more likely, after it is impacted by a larger trigger such as the movement of one of the surface slabs. Below 7500 feet the avalanche danger is expected to be Moderate where initialy small wind slabs grow in size and sensitivity throughout the day in steep avalanche paths prone to wind loading.
