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Avalanche Forecast

Archived

Mar 7th, 2023–Mar 8th, 2023

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

Coquihalla, Harrison-Fraser, Manning, Skagit.

Lingering wind slabs may remain reactive to human triggers on a variety of aspects at treeline and above.

Avoid travelling on slopes below cornices.

Confidence

Moderate

Avalanche Summary

No new avalanches were reported in this region on Monday.

On Saturday, explosive avalanche control work resulted in numerous very large avalanches. They included storm, persistent, and deep persistent slab avalanches and were size 3-4. They initiated on a variety of aspects in the alpine.

Snowpack Summary

Cornices are large and may fail with daytime heating.

Sun crust on sunny aspects. Up to 100 cm of snow last week and shifting strong winds formed wind slabs on a variety of aspects at treeline and above. These slabs are sitting on either hard surfaces or small facets.

A crust formed in mid-January can be found down 90 to 130 cm. In areas around the Coquihalla, facets can be found sitting on the crust. This layer is of greatest concern with large triggers, such as a cornice fall, or by first triggering a smaller avalanche that could step down to this interface.

Weather Summary

Tuesday Night

Mostly clear skies / Light south ridgetop wind / Low temperature at treeline -12 C / Freezing level valley bottom.

Wednesday

Mostly sunny / Light southeast ridgetop wind / High temperature at treeline -1 C / Freezing level 1300 m.

Thursday

Sunny / Light southeast ridgetop wind / High temperature at treeline -2 C / Freezing level 1100 m.

Friday

Cloudy with flurries; 3-5 cm / Light southeast ridgetop wind / High temperature at treeline -4 C / Freezing level 800 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be especially cautious as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Avoid exposure to slopes that have cornices overhead.
  • Be alert to conditions that change with elevation and sun exposure.

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.

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.