Avalanche Forecast
Regions: Olympics.
In the Olympics, the main problem has shifted to new areas of wind slab on lee wind exposed terrain, near and above treeline. Wind slabs may have formed on a variety of aspects due to highly variable wind directions. Watch for new cornices near ridges.
Detailed Forecast
Cool weather with light snow showers and moderate westerly winds should allow for an overall slowly decreasing danger.Â
The greatest avalanche problem should be sensitive wind slabs on lee slopes, mainly W-N-E facing slopes, especially below ridges, near and above treeline.Â
Watch for newly formed cornices along ridges as well. These may be sensitive to human triggers.
Below treeline, the old wet snowpack should continue to drain, and refreeze forming a new crust. Watch for open creeks which were reported to be quite deep in areas, below treeline.Â
Snowpack Discussion
Heavy rain fell in the Olympics Wednesday afternoon through Thursday morning to at least 7500 feet. Over 2 inches of rain was recorded at the Hurricane Ridge weather station by Thursday midday.  This rain event should give the snowpack a new horizon going forward.Â
A strong cold front passed the area Friday depositing about 6-8 inches of new snow by Friday afternoon. The new snow has fallen with very strong and shifting winds creating both new shallow wind slabs near ridges and sensitive new cornices.
NWAC observer, Matt Schonwald travelled near and below treeline Friday and found cracks in the newly forming wind slabs on a variety of aspects due to swirling winds. Also, new cornices were sensitive to trigger, but still relatively small.
As expected in this region, the bonding of the new snow to the forming crust was reportedly very strong. There was, however, a thin layer of low density stellar crystals above the crust, forming the weak layer for newly forming wind slabs to fail.
These conditions should produce some sensitive human triggered avalanches on wind loaded terrain until those layers have time to settle and stabilize, mainly near or above treeline.
In the below treeline zone, a strong crust with shallow new snow should allow for improving conditions, but watch for shallow wind deposited snow on isolated features, such as cross loaded ribs or slopes convexities.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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
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, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1