Avalanche Forecast
Regions: Olympics.
Deep areas of wind and storm slabs should make triggering an avalanche in steep terrain possible or even likely. Avoid travel on steep slopes receiving wind deposited snow, where fresh wind slab deposits will be sensitive to human triggering. Expect dangerous avalanche conditions at mid and upper elevations. Choose conservative terrain.
Detailed Forecast
A band of enhanced snow showers should arrive Friday night with diminishing showers Saturday. This should freshen storm snow with winds continuing to redistribute new cold snow to lee slopes by Saturday.Â
This weather should cause widely variable snow conditions with some wind exposed slopes scoured to recent crusts and lee slopes building deeper wind drifts and slabs. Watch for changes in snow conditions, particularly stiffer more dense snow, likely a wind or storm slab. Avoid travel on slopes if you encounter wind stiffened surface snow, especially on steeper exposed terrain and steep roll-overs. Â
The temperatures should remain cool, depositing new low density snow that will be easy for winds to re-distribute on exposed terrain. Â
Wind slabs near and above treeline remain the primary avalanche problem in this area, so remain conservative in your terrain choices especially as you venture into exposed terrain.
The best and safest snow will remain in sheltered terrain away from ridges.Â
Snowpack Discussion
A strong storm Wednesday through Thursday followed by cool showery weather Friday has deposited about 2 ft of storm snow as of Friday afternoon. The new snow fell at cooling temperatures causing a favorable density profile with colder looser snow over denser warmer snow in wind sheltered terrain.
However, strong winds Wednesday night with moderate winds Thursday and Friday have significantly re-distributed new snow in exposed terrain. This has built unstable storm and wind slabs in much of the terrain near and above treeline. These slabs are sensitive to human triggering on exposed steep terrain, especially on NE-E facing slopes that have received the greatest wind loading. Wind deposited slab layers in the most favorable terrain are likely to be 2-3 ft thick or more.Â
The interface of the storm snow to the old wet snow is good currently with a slowly strengthening rain crust forming below the storm snow.Â
The older snow is well settled and strong with various melt-freeze and rain crust layers throughout.Â
The height of snow across the terrain is quite variable with little snow in many areas below treeline. Numerous obstacles still exist at all elevations.
Observations
NWAC observer Matt Schonwald traveled in the Hurricane Ridge terrain Thursday, Jan 18. Matt found excellent right side up fresh snow of about 8 inches by Thursday afternoon that was bonding well to the underlying old wet snow and unreactive to human triggering in wind sheltered terrain.
In wind exposed terrain however, winds Thursday were actively transporting new snow and building sensitive slab layers. These reactive wind slabs were found mostly on NE-E facing terrain, mostly in the 6-8 inch range. Â Slabs were most sensitive in the mid-slope terrain and on steep wind rolls.
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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: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1