Avalanche Forecast
Issued: Dec 12th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
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VIAC
Pay attention to conditions that change with exposure to wind. Maintain margins around wind-drifted features, particularly near ridges and roll-overs.
Summary
Confidence
Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Forecast snowfall amounts are uncertain.
Weather Forecast
A short burst of southeast wind on Monday
Sunday night: Partly cloudy, 5-15 cm of snow above 500 m, winds becoming southeast and increasing to moderate, treeline temperatures near -5 C.
Monday: Partly cloudy, 5-15 cm snow above 500 m, moderate southeast winds easing to light, treeline temperatures near -4 C.
Tuesday: Clearing trend, 5-15 cm of snow above 300 m overnight, light southwest wind, treeline temperatures near -6 C.
Wednesday: Cloudy, 5-15 cm of snow above 600 m, strong southeast winds, treeline temperatures near -4 C, freezing level rising to 700 m.
Avalanche Summary
On Saturday, there were reports of numerous small (size 1-1.5) avalanches releasing 30-70 cm deep in the storm snow across a variety of aspects. See this MIN report from the Mt. Washington area for a helpful visual.
Snowpack Summary
An impressive storm over the weekend brought 50-90 cm of snow to the mountains. A gradual rise in temperature during the storm formed a crust layer that can be found in areas up to 1400 m. An additional 20-50 cm of snow has accumulated since temperatures cooled. Strong southwest winds have had an ample supply of snow to drift into wind slabs at upper elevations. It remains possible to trigger these wind slabs in lee terrain features, such as down-wind of ridges and roll-overs. A shift in wind direction from southwest to southeast on Monday may form fresh reactive wind slabs in a tricky cross-loading pattern. Monitor for changing conditions as you move into wind-exposed terrain and pay attention to cracking or hollow sounds.
Below the early December crust layers, the snowpack is generally well-settled. With this storm event, a greater number of areas below treeline are meeting threshold snow depths for avalanches.Â
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be aware of highly variable recent wind loading patterns.
- Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
Problems
Wind Slabs
Strong southwest winds and recent snow have formed wind slabs in lee terrain features at upper elevations that may remain possible to trigger. With winds shifting to the southeast, there is potential for fresh slabs to build in a cross-loaded pattern.
Aspects: North, North East, East, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 13th, 2021 4:00PM
