Avalanche Forecast
Regions: Olympics.
Recent wind and isolated storm slabs may linger Thursday, but slowly stabilize. Also, watch for local cornices along ridges. Be prepared to alter plans if local snow and avalanche conditions warrant.
Detailed Forecast
Another break between systems is expected Thursday as brief high pressure transits the region. There may be a few light showers early Thursday, but little accumulation is expected. Winds should be light Thursday.
This should allow for recent storm snow and any wind slabs below ridges to begin settling.  The greater concern Thursday should be on steep lee slopes below ridges that may have wind deposited snow deposited Wednesday. These slopes should range from NW-NE facing.Â
In addition, watch for recent cornice formations along ridges and give these early season cornices a wide birth as they may be fragile. Â
In much of the lower elevation, below treeline band, there is insufficient snow to produce avalanches, but watch for early season hazards such as rocks and creeks.  Avalanche problems should be limited to the upper part of this elevation band and higher elevations.
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Snowpack Discussion
Most recent storm began about midnight Wednesday, Nov. 30 with new snow at Hurricane Ridge about 12-14 inches as of late Wednesday afternoon. Winds initially were moderate southerly, shifting to more westerly and diminishing greatly by Wednesday afternoon.
A nice report was received via the NWAC website (Observations tab) for Saturday in the Hurricane Ridge area. In summary, pit tests gave only a low quality shears or collapses and an ECT test that did not indicate any propagation. Loose dry avalanches were indicated as the main concern.
On Sunday morning the Hurricane rangers reported 7 inches of new snow. They reported that a snowboarder on Saturday triggered a small loose dry snow avalanche on the Sunrise run, a steep slope that faces northeast at about 5200 feet.
No observations were submitted on Monday, but another 4 inches accumulated above 5000 feet in the Hurricane Ridge area with generally light WNW winds recorded at the NWAC weather station. Tuesday was a break between weather systems.Â
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: 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, North West.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1