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Avalanche Forecast

Archived

Mar 22nd, 2022–Mar 23rd, 2022

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

Regions

Northwest Inland.

A crust on the surface will make triggering an avalanche less likely but we still have uncertainty about a buried weak layer. Wind slabs likely remain triggerable at elevations where snow has remained dry.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Tuesday night: Flurries around 5 cm. Strong southwest wind. Alpine high around -8 °C. Freezing level dropping to valley bottom.

Wednesday: A mix of sun and cloud. Moderate southwest wind. Alpine high around -6 °C. Freezing level 1000 m. 

Thursday: A mix of sun and cloud. Light southeast wind. Alpine high around -5 °C. Freezing level 1000 m.

Friday: A mix of sun and cloud. Light south wind. Alpine high around -4 °C. Freezing level 1200 m.

Avalanche Summary

On Monday, natural and skier controlled wind slabs size 1.5 were reported. Over the last two days large, (size 2-3) avalanches have resulted from natural cornice failures triggering wind slabs on slopes below.

Persistent slab avalanches on a weak layer of surface hoar crystals buried in late February surprised a few people last week with accidental and remote triggers. The layer was most active on north-northeast aspects between 1200 and 1600 m in areas north of Hazelton.

Snowpack Summary

Wet surfaces up to 1700 m have likely refrozen into a crust. Wind slabs may be found at high elevations that remained dry.

A couple of layers of weak crystals exist in the upper snowpack, most often found on north to east aspects around treeline. We suspect that the surface crust will help bridge these layers, decreasing their likelihood of triggering.

A thick crust formed in mid-February is now buried 50-80 cm deep. It is unlikely to present an avalanche problem under the current conditions and in fact bridges any underlying instabilities in the lower snowpack.

Terrain and Travel

  • A crust on the surface will help bind the snow together, but may make for tough travel conditions.
  • Watch for areas of hard wind slab on alpine features.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Carefully evaluate bigger terrain features on an individual basis before committing to them.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.

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.