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Archived

Avalanche Forecast

Dec 13th, 2015–Dec 14th, 2015
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
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.

The strong storm Saturday, and subsequent additional snowfall Sunday should maintain widespread wind and storm slab layers on lee slopes near ridges Monday. Travel conservatively by staying off or below steeper slopes and avoid wind loaded terrain, especially but not limited to northwest through southeast facing terrain.

Detailed Forecast

A few isolated snow showers may linger Monday, while winds should be light and temperatures remain cool. 

This should allow for a slowly improving avalanche danger as recent storm and wind slabs begin settling and stabilizing.

However, storm and wind slab conditions should remain sensitive or still likely to trigger in specific areas and more widespread areas above treeline from very strong winds Saturday. North to east facing lee slopes will continue to be loaded and slower to stabilize.  

Dangerous avalanche conditions are expected above tree line requiring conservative decision-making and cautious routefinding.

Be cautious with any steeper open terrain suspected of recent wind loading, leaving those more exposed features a wide margin of safety.

Snowpack Discussion

After a wet week that culminated with heavy rain Monday and Tuesday, melting the Waterhole snowdepth (5000 ft) down to around 18 inches, winter has returned to lower snow levels and new snow. The NPS ranger at Hurricane Ridge reported a snowdepth of 44 inches Sunday morning with 28 inches new snow received since Tuesday.  

Avalanche and Snowpack Observations

NWAC pro-observer, Matt Schonwald was at Hurricane Ridge Friday, collecting the first snowpack observations in the Olympic zone for NWAC this season, welcome Matt! The snowdepth averaged around 1 meter (over 3 ft) with slightly more snow in less wind affected areas. The most recent snow has bonded well to the old surface and there were no significant storm snow instabilities. However, there were signs of significant wind loading onto open lee NE slopes, mainly applicable in the near and above treeline elevation bands.  Another strong storm Saturday, with very strong winds and snow, followed by additional snow Sunday, but with lighter winds has changed the upper snowpack significantly since Friday. An additional 15-20 inches have accumulated since Friday. A report by Park Ranger at Hurricane Ridge Sunday midday reported a soft slab release below the Sunrise Ridge area near Hurricane. The slide was likely triggered, however that was not confirmed.  The avalanche crown was estimated at 2-3 ft and released about 150 wide and ran about 100 feet vertical, certainly big enough to get into serious trouble. Terrain anchors are rapidly being buried by recent snowfalls but may still add significant anchoring in many areas below 4-4500 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, North West.

Elevations: Alpine, Treeline.

Likelihood: Likely

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: All elevations.

Likelihood: Possible

Expected Size: 1 - 1