Avalanche Forecast
Regions: Olympics.
Watch for left over wind slab on Saturday which may get covered by less cohesive snow Friday night.
Detailed Forecast
West winds will slightly decrease but not let up on Saturday with mostly light snow showers much of the day and cooler temperatures. However alpine west winds and snow should begin to increase in the afternoon as the next system approaches.
Shallow wind slab from Friday may linger on Saturday mainly on northwest to southeast slopes in the near and above treeline. Watch for firmer wind transported or hollow sounding snow. Wind slab from Friday may get covered by less cohesive snow Friday night making it harder to detect the underlying wind slab layer.
Avoid ridges that have a cornice and slopes below cornices.
Be prepared to change your plans if the next storm begins to arrive and significant snow begins to accumulate sooner than expected on Saturday afternoon.
In most of the lower part of the below treeline band there is still insufficient snow for avalanches but watch for early season hazards such as terrain traps, rocks and creeks.
Snowpack Discussion
A bit of a break was seen Thursday with snow showers tapering with 1 an inch of new snow at Hurricane ending Friday morning.
NWAC pro observer Matt Schonwald visited Hurricane on Thursday and reported lots of wind effects but a generally well bonded snow pack and snow profiles in pits that lacked a slab structure. The snow was found to be unconsolidated at lower elevations making terrain traps and creek crossings a hazard.
A front is crossing the area on Friday causing moderate to strong south to west alpine winds in the Olympics and Washington Cascades, hopefully with several inches of new snow at Hurricane and a warming trend.
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.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1