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Archived

Avalanche Forecast

Jan 17th, 2013–Jan 18th, 2013
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
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Northwest Inland.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Overnight Thursday and Friday: Moderate snowfall becoming light on Friday / Strong to extreme southwest winds becoming moderate and northwesterly / Alpine temperatures at about -4.0Saturday: Light snowfall / Moderate west winds /  Alpine temperatures at about -2.0Sunday: Mainly dry conditions / Light southwest winds / Alpine temperature of about -1.0

Avalanche Summary

Due to inclement weather, observations have been limited; however, on Monday a size 2 windslab avalanche was skier-triggered in a chute above Crater Lake. The crown was about 30m wide with a maximum height of 80cm. On Tuesday a snowmobiler triggered a size 1 windslab on a slope which was reported to be "normally very stable". Forecast weather suggests that there will be ongoing windslab activity.

Snowpack Summary

Rain below treeline has continued to maintain moist surfaces at lower elevations. Moderate amounts of new snow and strong winds at higher elevations have most likely formed hard windslabs in the lee of terrain breaks and ridges.A surface hoar layer that was buried at the end of December is now down 60-80 cm, and was reactive in some areas with recent warming. An otherwise strong mid-pack overlies a weak base layer of facets/depth hoar and the remnants of a crust.

Avalanche Problems

Wind Slabs

Strong westerly winds have created windslabs on lee terrain. With forecast snowfall and higher than normal wind values, watch for continued loading lower on the slope and in other unsuspecting locations.
Be aware of the potential for wide propagations due to the presence of hard windslabs.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 4

Persistent Slabs

Forecast snowfall will add additional load to buried weak layers. Watch for triggering in sheltered, unsupported terrain.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 4

Deep Persistent Slabs

A deeply buried facet/crust weakness exists near the base of the snowpack. This layer could be triggered by large loads such as a cornice collapse or from a thin-spot trigger point.
Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 5