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Archived

Avalanche Forecast

Dec 9th, 2020–Dec 10th, 2020
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Glacier.

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

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

Avalanche Problems

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

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