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Archived

Avalanche Forecast

Dec 22nd, 2017–Dec 23rd, 2017
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

Storm snow received earlier this week continues to stabilize with no recent natural or human triggered avalanches reported. Watch for areas of wind transported snow forming winds slabs on a variety of aspects. Wind slab will not be listed below treeline, but allow for the possibility of isolated areas of firmer wind transported snow in upper portion of the below treeline band. 

Detailed Forecast

Cold temperatures and fair weather will continue to allow stabilization on the upper snowpack on Saturday. As the avalanche danger continues to decrease keep an eye out for signs of unstable snow in isolated terrain such as unsupported slopes. 

Watch for wind transport of snow Saturday as winds increase and change directions forming new winds slabs on a variety of aspects. Identify evidence of wind loaded snow such as drifts and new cornices near ridgeline and mid-slope cross-loaded features. Give these fresh wind slabs a wide berth. Wind slab will not be listed below treeline, but allow for the possibility of isolated areas of firmer wind transported snow in upper portion of the below treeline band.

Early season snow conditions still exist. Be particularly cautious of creeks as many of them have not become snow covered for the winter.

 

 

Snowpack Discussion

A few inches of new snow fell in the Hurricane Ridge area on Friday adding to the week’s already impressive snow totals. Cool and fair weather allowed much of the upper snowpack to stabilize Wednesday and Thursday resulting in a decrease in the avalanche danger.

Winds likely redistributed snow near ridge crest and in exposed terrain Wednesday and Thursday. Wind slabs were most likely formed on a variety of aspects near and above treeline.

In general about two feet of snow now sits on the old snow surface from a week ago.

Observations

On Friday, Olympic NPS rangers reported no recent avalanche activity in the Hurricane Ridge area. Limited snowpack observations in the area continue to support a stabilizing upper snowpack.

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: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1