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Avalanche Forecast

Archived

Mar 21st, 2020–Mar 22nd, 2020

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

Regions

Northwest Coastal.

Fresh storm slabs will build as 15-25 cm of new snow falls through the day Sunday. Human triggering will be especially likely where new snow has been wind-loaded into lee terrain features and where it sits over a crust.

Confidence

High -

Weather Forecast

Saturday night: Clear. Moderate northwest wind. Freezing level 1000 m.

Sunday: 15-25 cm new snow. Light to moderate southwest wind. Freezing level 600 m.

Monday: Scattered flurries bringing up to 5 cm. Light northeast wind. Freezing level 1000 m.

Tuesday: Flurries. Light north wind. Freezing level 1000 m.

Avalanche Summary

Natural loose wet avalanche activity has been observed on sun-exposed slopes during the heat of the day over the last few warm days. A few cornices were also triggered by the warming. Glide slab activity has also been reported recently out of steep terrain where snow sits over smooth surfaces. 

If you decide to travel in the backcountry, consider sharing your observations with us and fellow recreationists via the Mountain Information Network (MIN) to supplement our data stream as operators are shutting down. Even just a photo of what the day looked like would be helpful.

Snowpack Summary

15-25 cm of new snow is falling over extensively wind-affected surfaces and over melt-freeze crusts on solar aspects and low elevations.

A layer of surface hoar crystals is buried around 40 to 80 cm in sheltered areas at and below treeline. See this MIN from the Shames area that shows this layer when it was on the surface, prior to burial on March 9.

An early-season layer of faceted grains and a melt-freeze crust may linger at the base of the snowpack. A large load, such as a cornice fall, has the potential of triggering it.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Closely monitor how the new snow is bonding to the crust.
  • Keep in mind the crust offers an excellent bed surface for avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.