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Avalanche Forecast

Archived

Jan 21st, 2021–Jan 22nd, 2021

Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

Even with compact snow surfaces and cool temperatures, don't underestimate the power of the sun. Minimize exposure to slopes with cornices overhead when solar radiation is strong. Wind slabs are stubborn to trigger but a large load like a cornice fall might do it.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Thursday night: Clear, light wind, alpine low -8, freezing level valley bottom.

Friday: Sunny, light wind, alpine high -4, freezing level 500 m.

Saturday: Sunny with increasing cloud in the afternoon, light wind increasing to moderate northwest, alpine high -7, freezing level valley bottom.

Sunday: Flurries up to 5 cm, light wind, alpine high -9, freezing level valley bottom.

Avalanche Summary

No new reports in the last couple days. A few small wind slab avalanches were reported early in the week. Explosive control targeting cornices on Friday and Saturday produced size 2 results, some triggering deep slabs on the rocky slopes below. 

Earlier this month, we saw significant deep persistent slab activity, both natural and human triggered.

Snowpack Summary

Extensive wind effect in the alpine includes scoured windward aspects and hard slabs in lee terrain. Soft snow may be found in sheltered areas around treeline. A widespread surface crust exists below 1900 m and on south-facing slopes.

Remnants of a melt-freeze crust from early December may be found around 200 cm deep in the snowpack. Several large natural and human triggered avalanches failed on this layer earlier this month. Although it still shows propagation and collapse to moderate to hard loading in the most recent snowpack tests, it has become well bridged by overlying snow and crust.

Terrain and Travel

  • Minimize your exposure time below cornices.
  • Cornices become weak with daytime heating or solar exposure.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.

Problems

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.

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.