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Avalanche Forecast

Archived

Dec 8th, 2016–Dec 9th, 2016

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

Regions

Olympics.

Dangerous avalanche conditions should develop on Friday. Look for new wind slab near and above treeline. New snow may bond poorly to weak surface snow below treeline and become reactive by the end of Friday with increased loading and a gradual warming trend. Keep it conservative and expect increasing instability Friday. 

Detailed Forecast

Will we reach a tipping point on Friday with widespread sensitive slab development or will recent weak layers be buried and await the next storm to become active?  A first round of light snow Thursday night followed by increasing shower activity and a gradual warming trend Friday should lead to an increasingly sensitive snowpack.

Dangerous avalanche conditions should develop on Friday. Look for new wind slab near and above treeline on non-traditional lee westerly aspects. Also, new snow may bond poorly to weak surface snow and become reactive by the end of Friday with increased loading and a gradual warming trend. The near-treeline band should be the trickiest to navigate where shallow new wind slab may have already buried recent weak surface snow. 

In steep sheltered terrain continue to watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences.  

With deep unconsolidated snow in many wind protected areas, there is an increased risk for tree well and snow immersion suffocation at this time. Ride or ski with a partner and keep them in sight at all times!

Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks.

Snowpack Discussion

Weather and Snowpack

An active and cool weather pattern has resulted in a snowy December thus far with the Hurricane Ridge NWAC station recording about 3 feet of snow.

Cold and fair weather has taken hold since Monday. There have been many reports of right side up, favorable density profiles with lower density snow nearer the surface in the Cascades and we expect similar conditions in the Olympics.

Given the favorable snowpack profile, good bonds between older snow layers and a lack of deeper layer concerns, avalanche problems should be confined to the upcoming old snow/new snow interface or within new storm layering. 

In areas near and below treeline not affected by moderate easterly winds over the last 24 hours, near surface faceting and/or surface hoar should be widespread. 

Recent Observations

Recent moderate easterly winds have likely built new wind slabs on lee aspects near and below treeline in the Hurricane Ridge area with plenty of low density of snow available for transport. 

Problems

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.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.