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Archived

Avalanche Forecast

Dec 14th, 2015–Dec 15th, 2015
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
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.

Pay extra attention if you see winds transporting snow and find more than a few inches of snowfall on Tuesday.

Detailed Forecast

A weak cold front will cross the Northwest on Tuesday. This should bring northwest winds and light snow to Hurricane Ridge with a brief, slight rise in the low snow levels.

New small shallow areas of wind and storm slab are possible at Hurricane. Wind slab might be found on more south aspects due to northwest winds. Pay extra attention if you see winds transporting snow and find more than a few inches of snowfall.

Previous wind slab layers from strong winds Saturday should further slightly stabilize but could still be triggered on previous lee slopes.

Snowpack Discussion

An atmospheric river and warm very wet weather was seen last week. This caused consolidation and stabilizing of the older part of the Olympics snowpack with the Waterhole snowdepth dropping to around 18 inches.

A stormy pattern with cooling was seen late last week and over the weekend with about 2.5 feet of snowfall at Hurricane.

A Park Ranger at Hurricane Ridge Sunday midday reported a storm slab release below the Sunrise Ridge likely on an east facing slope near Hurricane. The slide was likely triggered but this was not confirmed.  The avalanche crown was estimated at 2-3 feet and released about 150 wide and ran about 100 feet vertical - big enough to get into serious trouble.

A dry, cool day at Hurricane on Monday will have brought some stabilizing.

Terrain anchors have been somewhat buried by recent snowfall but will still add significant anchoring below about 4000-4500 feet.  

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, South.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1

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: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1