Archived

Avalanche Forecast

Jan 6th, 2017–Jan 7th, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Northwest Inland.

Fresh wind slabs could be touchy and deep persistent slabs are lurking in shallow snowpack areas.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SATURDAY: Mainly cloudy with scattered flurries bring another 3-5 cm, temperature around -20, and moderate easterly ridgetop winds.SUNDAY: Cloudy with sunny periods, temperatures reaching -10 C with a strong alpine temperature inversion, and light southeasterly ridgetop winds.MONDAY: A mix of sun and cloud with isolated flurries, temperature around -15 and light to moderate easterly ridgetop winds.

Avalanche Summary

Reports from Wednesday and Thursday include two more deep persistent avalanches. One Size 2 and one Size 3 both running on facets at the base of the snowpack south facing alpine slopes. These deep persistent slabs will remain a concern, as it is possible to trigger large avalanches.

Snowpack Summary

A light dusting of snow has likely buried recently formed surface hoar and/or facets. Snow depth at treeline varies from about 1 m in most areas to 2 m at deeper snowpack areas in the south and west of the region, and up to 250 cm in the alpine. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard wind slabs. These wind slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 20-30 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be lurking close to the ground nestled in amongst the facets.

Avalanche Problems

Wind Slabs

Wind slabs continue to be a concern for human triggering. Recent extreme winds have stripped some exposed north and east aspects and created variable depth deposits on south and west aspects.

Be cautious as you transition into wind affected terrain.Avoid travelling in areas that have been reverse loaded by winds.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Deep Persistent Slabs

The lower snowpack is predominantly weak facetted crystals above a rain crust that developed in November. There are a couple of layers of concern in the mid snowpack, but I suspect that avalanches in motion may step down to the crust or smooth ground

Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3