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Avalanche Forecast

Dec 4th, 2019–Dec 5th, 2019
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
Alpine
4: High
The avalanche danger rating in the alpine will be high
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

Regions: North Columbia.

Storm snow totals have varied across the region, with field observations reporting deeper layers in the snowpack being becoming more reactive. Conservative terrain choice is recommended until the distribution of weak layers is better understood.

Confidence

No Rating - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday night: Cloudy with clear periods. Alpine temperature -8 C, west wind 10-20 km/hr.

Thursday: Cloudy with scattered flurries, trace to 5 cm. Alpine temperature -4 C, south wind 20-30 km/hr.

Friday: Snow, 10-30 cm. Alpine temperature -3 C, southwest wind 25-35 km/hr.

Saturday: Snow, 10-20 cm. Alpine temperature -4, southwest wind 20-30 km/hr.

Avalanche Summary

On Wednesday, storm snow continued to be reactive to skier traffic, including triggering slab avalanches to size 2 and cracking on small, supported slopes. A couple of field observations reported slab avalanches failing on a layer of surface hoar (down 60-80 cm) at treeline elevations.

On Tuesday, a natural avalanche cycle was observed in Glacier National Park. Numerous size 2 storm slab avalanches were observed on all aspects at 2200 m and above. Additionally, 2 size 3 storm slab avalanches were observed on a north aspect at 2165 m and a northwest aspect at 2400 m. Near Revelstoke, storm slab avalanches to size 2 were reacting easily to explosives, many occurring on north and northeast aspects from 1800-2300 m.

Snowpack Summary

Storm snow totals reached 25-50 cm along with moderate westerly winds. Slabs have formed in areas exposed to wind.

The new snow covered a faceted upper snowpack and previously wind-affected surfaces, and surface hoar in sheltered areas around treeline and below.

Down 60-80 cm, below the old, wind affected snow, a layer of surface hoar (feathery crystals) may be found in sheltered areas around treeline. In these areas old, stubborn wind slabs may still be reactive where they overly the weak surface hoar on a crust.

A variety of crusts from late October are buried deeper in the snowpack. Total snow depths range from 100-170 cm around tree line.

Avalanche Problems

Storm Slabs

Upwards of 30-50 cm new snow accumulated in the last storm. Reactive storm slabs developed, especially in areas affected by wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2.5

Persistent Slabs

A surface hoar/crust, down 60-80 cm has become reactive with the recent storm snow. This layer is most likely found in sheltered openings around treeline and below. 

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood: Possible

Expected Size: 1 - 2.5