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Archived

Avalanche Forecast

Dec 22nd, 2014–Dec 23rd, 2014
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
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

Regions: Mt Hood.

Avoid steep previous lee slopes with firmer wind transported snow from the recent storm mainly in the above treeline band Tuesday.

Detailed Forecast

Partly cloudy weather Tuesday morning should give way to mostly cloudy weather in the afternoon. This is not likely to create significant new layers by Tuesday afternoon.

Watch for wind slab from the previous storm that will be most likely to linger on steep north to southeast slopes in the above treeline band.

Increasing winds and increasing rain or snow may begin to create new layers Tuesday night.

Snowpack Discussion

A strong warm storm moved over the Northwest Saturday and Sunday. Winds were seen to over 100 mph at some locations. Especially strong winds and heavy precipitation was seen at Mt Hood. Precipitation fell as snow mainly in the above treeline zone Saturday and Sunday.

No avalanches were reported Saturday or Sunday probably due to the horrific weather conditions and lack of back country travel.

Decreasing winds and a little cooling were seen at the tail end of the storm Sunday night and Monday early morning with about 5-10 inches of new making it down to NWAC weather stations in the near treeline zone. No avalanches have been reported so far Monday and conditions will have partly stabilized.

Some lingering wind slab and storm slab are likely mainly in the above treeline zone on Monday.

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, Treeline.

Likelihood: Possible

Expected Size: 1 - 1