Strong winds and heavy snowfall will increase the hazard and create very dangerous avalanche conditions above an elevation of 8,000 feet. Large to very slab avalanches may release naturally or be triggered by humans. These dangerous avalanches could run long distances. Travel in avalanche terrain is not recommended during periods of high hazard. The hazard will be on the increase at the lower elevations where new wind slabs will begin to form on steep slopes.
Strong west to southwest winds will be increasing the load on persistent weak layers in the snowpack that has poor structure and a history of producing large avalanches. Avalanche activity is likely today on steep slopes. These slides could be up to 3 feet deep. They may release naturally, be remotely triggered from flat areas below slopes or be triggered by humans who venture on to steep slopes.
New soft slabs will begin to form on leeward aspects. These slabs could grow to depths of 6 to 18 inches by the end of the day. These fresh slabs could be human triggered on steep slopes and could step down to deeply buried layers of faceted snow at the higher elevations and on northeast through northwest aspects down to an elevation of 8,000 feet.
( Discussion is generated from the previous day's afternoon forecast. )An unsettled progressive zonal flow will be the defining feature of the weather though Saturday. A series of shortwaves or ripples in the westerly flow will precede the passage of the main trough on Friday. A winter storm warning is in effect for the mountains of Western Wyoming and Eastern Idaho. A brief break in the snowfall will occur this evening until after midnight when a stronger source of moisture begins to plow into the region. Heavy snowfall is expected to develop in the early morning hours and continue through the day and into the evening. Snowfall totals 1 to 2 feet are likely in the mountains by Friday morning. This snow event will be accompanied by strong winds and mild temperatures. Winds in the mountains will be from the west to southwest at 20 to 30 with gust from 40 to 50 miles per hour. Temperatures will be in the 20's in the mountains and rise into the mid-30’s in the valleys.The new snow and wind will increase the avalanche hazard at all elevations. At the mid and upper elevations an extended loading period will likely cause very large avalanches to fail on the November drought layers. These dangerous slab avalanches are likely to be easily triggered by humans, fail naturally and may run long distances. Up there the general avalanche hazard rating is expected to increase from considerable to high. Travel in avalanche terrain is not recommended during high avalanche hazard conditions. At the lower elevations the general avalanche hazard is expected to increase from low to moderate. Down there, be aware of increasing hazard on steep wind loaded slopes and the potential for very large avalanches at the higher elevations to run into avalanche runout zones in the lower elevations.
