Avalanche Forecast

Issued: Dec 9th, 2020 8:00AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs and Deep Persistent Slabs.

Percy Woods,

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Glacier.

The storm is over leaving a touchy storm slab over surface hoar combo. Cautious, conservative route selection is required today.

Summary

Weather Forecast

Mainly cloudy with isolated flurries and a trace of precipitation.

Alpine temperatures reaching up to -4C with light westerly winds.

Freezing level up to 1600m today.

Cloudy with sunny periods Thursday and Friday with light winds, no precipitation and alpine highs of -9C.

Snowpack Summary

35cm+ of warm snow and mod/strong SW winds have formed a storm slab. It sits on a significant widespread surface hoar (SH) layer at tree-line and lower elevations. In the alpine, the storm slab rests on a crust on steep solar aspects. Several SH layers exist in the mid-upper pack, while the Nov 5 crust lurks as a deep persistent weakness.

Avalanche Summary

Yesterday natural avalanche activity to size 3.5 was observed in the highway corridor. Avalanche control produced avalanches to size 3.5. A MIN report yesterday of a skier remote size 1 from 15m distance in Teddy Bear Trees also shows the sensitivity of the buried surface hoar layer.

Confidence

Due to the number of field observations

Problems

Storm Slabs

An icon showing Storm Slabs

A 30-40cm cohesive storm slab has formed. It sits on widespread surface hoar (SH) or on a crust on steep solar aspects. Locations of large SH will be particularly touchy (below tree-line).

  • Watch for whumpfing, hollow sounds, and shooting cracks.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Storm slab avalanches may carry enough mass to overload the Nov 5 crust deep persistent weak layer. If this occurs expect to see  very large avalanches running to valley bottom.

  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3.5

Valid until: Dec 10th, 2020 8:00AM

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