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Archived

Avalanche Forecast

Dec 4th, 2015–Dec 5th, 2015
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

Regions: Olympics.

Deteriorating conditions along with increasingly dangerous avalanche conditions are forecast by Saturday afternoon. The terrain you started your day with may not be safe on the way out, so choose your travel plan wisely.   

Detailed Forecast

New storm and wind slab near and above treeline will be the focus Saturday. Moderate precipitation throughout the day along with increasing southwest winds should build new slabs on lee NW through E slopes. A warming trend throughout the day will also create unstable storm snow layers. 

Be prepared to curtail your plans if conditions deteriorate faster than expected. Human triggered natural slab avalanches are likely by the afternoon near and above treeline and on lee slopes.  

Early season hazards exist for much of the below treeline band throughout the Northwest, so ski and ride with caution. 

Snowpack Discussion

Manual observations from Hurricane Ridge and automated observations from the Waterhole Snotel show around 18-20" of snow near 5000 feet as of Friday. We have not received any snowpack observations from the Hurricane Ridge area for this season, but given the warmer temperature regime over the Olympics lately, we don't expect any persistent weak layer problems like those seen in the Cascades. Little new snow has been seen in the area this month, so recent storm and wind slab instabilities are expected to be minimal. 

Avalanche Problems

Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 1

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, North West.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 1