Avalanche Forecast
Regions: Cascades - North West.
Another 2 feet of snow and wind by the end of Tuesday will maintain dangerous conditions. Use caution on slopes over 35 degrees where the new snow slides easily. The most dangerous slopes will be near above treeline where the wind will drift new snow and where older stiff slabs are buried on sunny slopes.
Discussion
Snow and Avalanche Discussion
Avoid southeast through southwest slopes where you find stiff slabs below the snow surface.
The new snow has hidden older slabs, formed on February 9th, by north and east wind. This wind event created unusual wind loading patterns. On southeast through southwest aspect near and above treeline, these stiff slabs sit on a layer of weak sugary facets with an underlying crust. This was the snowpack structure at the site of a remotely triggered avalanche on Sunday (see photo). Use your probe to feel for very stiff snow at least 2 feet below the snow surface.
We received a report of a large, remotely triggered wind slab avalanche near Ptarmigan Ridge in the Mt Baker backcountry Sunday. This avalanche was approximately 2 feet deep and failed on a layer of sugary facets. Unusual avalanches like this should cause us to take notice. Avalanche Details: 2/10/19: SW aspect, 5200 ft. 45-degree slope.
Photo: Remotely triggered wind slab from Sunday.Â
Snowpack Discussion
New Regional Synopsis Coming Soon
Avalanche Problems
Storm Slabs
Use extra caution around any slope steeper than 35 degrees if you see the new snow sliding easily. Avoid drifts and steer around areas where the wind has stiffened the snow on leeward slopes at upper elevations. These slopes could produce larger and more dangerous avalanches. Use small test slopes to check how well the snow is bonding.
1.5 feet of warmer, more cohesive snow will fall on softer storm snow from the past 3 days. This will build a classic "strong-over-weak" layering, making slab avalanches easy to trigger. Southwest wind will form deeper drifts near and above treeline. The new snow has hidden older stiff wind slabs. Avoid southeast through southwest slopes where you find stiff slabs, about 2 feet below the surface, resting on weak facets.
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: Likely
Expected Size: 1 - 1