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Avalanche Forecast

Archived

Apr 8th, 2021–Apr 9th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

Avoid freshly wind-loaded features, especially near ridge-crests, roll-overs, and in steep terrain, and minimize exposure to cornices.  

Confidence

Low - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Thursday night: Cloudy, 5-10 cm of snow, strong southwest wind, treeline temperatures near -8 C, freezing level dropping to valley bottom overnight.

Friday: Mainly cloudy, scattered flurries with up to 5 cm of accumulation, moderate southwest wind, treeline temperatures near -4 C, freezing level rising to 800 m and dropping to valley bottom overnight.

Saturday: Increasing cloud, moderate west wind, treeline temperatures near -4 C, freezing level reaching 500 m and dropping to valley bottom overnight.

Sunday: Mix of sun and cloud, light west wind, treeline temperatures near -1 C, freezing level rising to 1000 m and dropping to valley bottom overnight.

Avalanche Summary

Since Monday, operators have reported small (size 1) natural and human triggered wind slabs on north and northeast aspects in the alpine. With new snow and wind in the forecast, wind slabs have the potential to be more reactive and more consequential.

Snowpack Summary

An incoming storm is expected to bring 5-15 cm of new snow by Friday afternoon accompanied by strong southwest winds. The new snow will add to fresh wind slabs that have been forming throughout the week from incremental accumulations and that may be up to 30 cm deep in some areas.

The recent snow has covered a variety of previous snow surfaces, including widespread wind-affect and a crust on steep south-facing slopes and at lower elevations. Cornices are large and looming at this time of year. 

Buried 70-120 cm deep, a spotty layer of surface hoar may exist on sheltered north aspects, but no recent avalanches have been reported on this layer. 

The lower snowpack is reported as well settled and strong in most areas. However, weak facets exist at the base of the snowpack in the more shallow snowpack zones across the region. Where it exists, this layer has the potential to be triggered on steep, rocky slopes with a shallow or thin to thick snowpack; especially with large loads such as a cornice fall.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Minimize your exposure time below cornices.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.