Avalanche Forecast
Regions: Olympics.
Wind slab formed last weekend should be stubborn to trigger except in isolated areas, but continue to watch for these layers.
Detailed Forecast
The clear weather over the past few days has given way to increasing clouds and a return to a few light showers. More clouds and light snow showers are expected Monday.Â
While wind slabs formed last week may be much more stubborn to trigger, continue to watch and test for these layers, on a variety of exposures. Look for recently transported snow further downslope from ridgelines than you might expect.
This weather should continue to allow the older wind slab to continue to slowly settle and stabilize. Wind slab will most likely be found on north to southeast aspects near and above tree line. Watch and test for inverted strong over weak storm snow.
Avoid venturing onto and below recent large cornices.
Snowpack Discussion
Cool, mostly dry weather over the past few days with sunshine and mild afternoon temperatures have allowed for further snowpack settlement and created thin, sun or melt freeze surface crusts on exposed slopes. No field orbs have been received since last weekend.
A cool, very snowy storm cycle brought about 4 feet of snowfall to Hurricane the week ending December 24th. Light additional accumulations in the past week have allowed the snowpack to slowly settle, however, surface snow conditions have changed due to the sunshine, warming and wind redistribution on many exposed slopes. Â
The wind slab that formed and observed last week should be much more difficult to trigger after a week of settlement. Â
The most recent observations were made Sunday the 27th by NWAC pro observer, Matt Schonwald who found a wide distribution of wind slab along ridge features as well as cross loaded slopes below ridgeline.  Matt ski cut a wind slab on a steep convex feature on a north facing slope at about 4800 feet. These features were evident on many exposed north to east facing slopes exposed to wind.
Â
Hurricane Ridge December 27, 2015. Triggered wind slabs on a steep convex north slope, 4800 feet. Photos T. Allen
See the short video illustrating the stiffer wind slab over the weaker underlying snow:Â
Â
Matt also reported that cornices were quite large overhanging some 2 meters in places and posed their own hazard due to their size. Unlike last year, there is now a healthy snowpack below treeline on all aspects.
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.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1