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Avalanche Forecast

Archived

Dec 16th, 2015–Dec 17th, 2015

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Olympics.

Dangerous avalanche conditions are expected by Thursday afternoon. Reign in your objectives later in the day as snowfall and winds increase by avoiding steep and wind loaded slopes, watching for sensitive storm layers. Recent and newly wind loaded slopes in the near and above treeline zone should be found on a variety of aspects Thursday. 

Detailed Forecast

A frontal system on Thursday should bring light to moderate snowfall in the Olympics along with a gradual warming trend.  

Avalanche problems will revolve around storm and wind slab. New and recent snow will be deposited on lee NW through NE aspects, although initially be wary of lingering wind slab on E-SE slopes from transport earlier in the week. Most avalanches should stay within the new storm snow, but a few may step down to older storm layers or crusts in isolated locations.    

As snowfall and winds increase, avoid steeper slopes and watch for increasingly sensitive storm layers. Rain should also activate storm slabs below and near treeline by Thursday afternoon. Generally avoid wind loaded terrain in the near and above treeline zone with new snow being transported to a variety of aspects.

The storm related avalanche danger will increase further Thursday night into Friday morning.  

Terrain anchors are still causing significant anchoring at the lowest elevations. Use caution near creeks which are still open in some areas.

Snowpack Discussion

An atmospheric river around Dec 9th pushed heavy rain above treeline in the Olympics. This caused consolidation and stabilizing of the older part of the Olympics snowpack. An active and cool weather pattern over the last week has produced about 2 to 3 plus feet of new snowfall near Hurricane Ridge that now sits over the 12/9 rain crust.

Last Sunday a NPS Ranger at Hurricane Ridge 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.

Cool weather with light new snowfall has been seen Monday through Wednesday. This will have allowed further consolidation and stabilizing of recent storm snow instabilities.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.

Wind Slabs

Wind Slab avalanches are the 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.