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Archived

Avalanche Forecast

Feb 9th, 2015–Feb 10th, 2015
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
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
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Olympics.

Avalanche danger should be limited to above treeline areas in the Olympics on Tuesday.

Detailed Forecast

The upper ridge will begin to rebuild over the west US on Tuesday. In the Olympics this should cause light west winds with light showers decreasing Tuesday morning and ending Tuesday afternoon.

Old wind slab in above treeline areas should be the main but unlikely problem in the Olympics. Reconsider this if there is more wind and snow than expected late Monday.

New storm slab seems unlikely due to limited new snow in the Olympics by Tuesday and will not be listed as a problem. Reconsider this if you find more than a few inches of new snow in above treeline areas on Tuesday.

As a result of the unseasonably low snowpack, especially at lower elevations, watch for terrain hazards such as open creeks, partially covered rocks and vegetation.

Snowpack Discussion

A series of fronts in an atmospheric river has been crossing the Northwest. Hurricane has seen about 5 inches of WE pretty much as rain from about February 5th-10th. About 10 inches of melting and consolidation was also seen at Hurricane.

The meager amounts of snow that remain in the Hurricane Ridge area are not currently creating an avalanche problem near or below treeline. South slopes at Hurricane are devoid of snow. On shaded or north slopes at Hurricane is there a couple feet of stable consolidated rounded grains or melt forms and crusts.

Some old wind slab might be possible in above treeline areas of the Olympics.

A filling low pressure system is crossing  mainly the south Cascades and Mt Hood area on Monday. This is causing the most wind and rain or snow in the far south Cascades and at Mt Hood on Monday. Lighter west winds and mostly light rain or snow showers in the Olympics will follow Monday night.

The mid and lower snowpack west of the crest should consist of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

Avalanche Problems

Wind Slabs

Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

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

Elevations: Alpine.

Likelihood: Unlikely

Expected Size: 1 - 1