Avalanche Forecast
Regions: Cascades - North West.
Give the snowpack time to adjust to the new snow. Use extra caution around slopes steeper than 35 degrees. The most dangerous avalanche conditions exist near above treeline where the wind drifts new snow and where older stiff slabs are buried on south and west aspects.
Discussion
Snow and Avalanche Discussion
The Mt. Baker area received over two feet of new snow (1.20in SWE) in the past two days, the majority of which fell overnight on Monday. The storm brought a slight warming trend and was accompanied by little wind. The new snow is very light, cold, and cohesionless in most areas. Natural and triggered loose dry avalanches were reported Tuesday in steep terrain near and above treeline. Natural slab avalanches were reported Tuesday as well - up to 12in thick and 50ft wide failing within new snow. Snowfall should taper off overnight, light to moderate winds will continue to blow from the southwest, and skies may clear by the afternoon on Wednesday.
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 aspects 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:
This large, remotely triggered wind slab avalanche occurred near Ptarmigan Ridge in the Mt Baker backcountry. The 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: SW aspect, 5200 ft. 45-degree slope. Lee Lazarra Photo
Snowpack Discussion
New Regional Synopsis Coming Soon
Avalanche Problems
Storm Slabs
Settlement and southwest winds will allow the new snow to form a more cohesive slab. Avoid drifts and steer around areas where the wind has stiffened the snow on leeward slopes at mid and upper elevations. Wind loaded slopes could produce larger and more dangerous avalanches. Continue to watch for loose dry avalanches - they could knock you off your feet or pile up debris deeper than you expect. If the skies clear Wednesday afternoon, expect loose wet activity on steep sun-exposed slopes.
Over two feet of new snow has fallen on low-density snow from the past few days. So far, the new snow has yet to form a cohesive slab. When it does, it may present a "strong-over-weak" layering, making slab avalanches easy to trigger. Use small test slopes to assess how the new snow is bonding to itself and older snow layers. The new snow has hidden older stiff wind slabs. Avoid southeast through southwest slopes where you find old stiff slabs below the surface resting on weak facets buried 2-3ft deep.
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