Archived

Avalanche Forecast

Dec 16th, 2012–Dec 17th, 2012

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

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

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

2: Moderate

The avalanche danger rating in the alpine will be moderate

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.

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

On Monday & Tuesday the region will see a cool unstable onshore flow with light SW winds, light snowfall with no significant accumulation, and freezing level near valley bottom. The next system is not arriving until sometime Wednesday when a Gulf of Alaska Low starts sliding south off the coast.

Avalanche Summary

On Wednesday last week, a snowmobile triggered a hard wind slab at the Sinclair snowmobiling area. It failed on the November crust/facet layer 30 cm above the ground while side hilling. This deep crust/facet layer has been the failure plane for a number of large avalanches further to the west and was suspected to have failed at the Hankin-Evelyn area last weekend.

Snowpack Summary

Storm snow instabilities are likely slowly settling and gaining strength. Spotty surface hoar was buried in the upper snowpack, particularly in sheltered treeline areas. New and buried wind slabs are widespread and exist on a variety of alpine and exposed treeline slopes due to variable winds. Of key concern is a November facet/crust layer which can be found near the base of the snowpack. This layer, which is widespread, can be triggered from thin-spot trigger points, or with a heavy load, such as storm slabs stepping down, a cornice fall or a snowmobile track digging a trench. It has the potential for large, destructive avalanches. . In general the snowpack depths, and therefore strength is highly variable due to windy conditions this season.

Avalanche Problems

Wind Slabs

Storm slabs might be encountered on steeper slopes with recent new snow. The bigger issue is linked to the wind. Be alert for new and buried wind slabs behind ridges and ribs.

Be cautious as you transition into wind affected terrain.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Use ridges or ribs to avoid pockets of wind loaded snow.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 4

Deep Persistent Slabs

A deeply buried facet/crust weakness exists. Very large and destructive avalanches may be triggered from thin snowpack areas or by heavy loads such as a storm slab stepping down, or a snowmobile spinning its tracks.

Carefully evaluate and use caution around thin snowpack areas.>Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 6