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Avalanche Forecast

Archived

Mar 27th, 2020–Mar 28th, 2020

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

Regions

Northwest Inland.

A reactive storm slab will build through the day as new snow accumulates with steady winds.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday night: Flurries, 5-10 cm. Alpine low temperature -7 C. Strong southwest wind.

Saturday: Flurries and snow, 5-15 cm. Alpine high temperature -5 C. Moderate to strong southwest wind.

Sunday: Flurries and snow, 10-15 cm. Alpine high temperature -7 C. Moderate southwest wind.

Monday: Cloudy with isolated flurries. Alpine high temperature -15 C. Moderate east wind.

Avalanche Summary

No new avalanche observations were reported this week, this comes from a very limited observation network. 

Snowpack Summary

Around 10-20 cm new snow is expected by the end of Saturday, falling with a steady wind. This will cover a mix of recent wind slabs and wind-affected snow as well as melt freeze crust on south aspects and below about 1100 m.

A weak layer of surface hoar crystals buried early March may be found around 30 to 50 cm deep, particularly in sheltered terrain around treeline. Recent observations of this layer are lacking.

An early-season layer of faceted grains and melt-freeze crust near the base of the snowpack likely lingers in high alpine features. The most suspect locations to trigger this layer would be where the snowpack is thin near rocky outcroppings. Large loads, such as cornice fall, may have the potential to trigger it.

Terrain and Travel

  • Watch for avalanche hazard to increase throughout the day.
  • Make conservative terrain choices and avoid overhead hazard.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.