Avalanche Forecast
Regions: Olympics.
Despite a favorable cooling trend with Saturday night's storm, westerly winds will build shallow wind slab on lee aspects. Look for wind slab development further downslope than you might expect due to locally strong winds and persistent loading.
Detailed Forecast
A strong frontal system will quickly sweep through the Olympics Saturday night. This system should deliver around 6 inches of snow to Hurricane Ridge. A cooling trend beginning Saturday night will continue through Sunday as shower activity quickly wanes later Sunday morning.Â
Despite a favorable cooling trend with this storm, westerly winds will build shallow wind slab on lee aspects near and above treeline. Look for wind slab development further downslope than you might expect due to locally strong winds and persistent loading. Watch for firm wind transported or hollow sounding snow.Â
Avoid ridges that have a cornice and slopes below cornices.
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
Weather and Snowpack
A front crossed the Olympics Friday with an inch of new snow reported by NPS rangers at Hurricane Ridge through Saturday morning. Post-frontal showers were generally light to moderate on Saturday and ridgetop winds were moderate out of the south. With the mild snow levels seen so far this season, most avalanche problems have been confined to the most recent storm layers found in the upper snowpack. Â
Recent Observations
NWAC pro observer Matt Schonwald visited Hurricane on Thursday and reported widespread wind effects but a generally well bonded snowpack 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.
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: All elevations.
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