Avalanche Forecast
Regions: Cascades - West.
Pay extra attention if you see winds transporting snow and find more than a few inches of snowfall on Tuesday.
Detailed Forecast
A weak cold front will cross the Northwest on Tuesday. This should bring northwest winds and mostly light snow with a brief, slight rise in the low snow levels.
New small shallow areas of wind and storm slab are possible mainly where the main snowfall is expected in the central Cascades. Wind slab might be found on more south aspects due to northwest winds. Pay extra attention if you see winds transporting snow and find more than a few inches of snowfall.
Previous wind slab layers from strong winds Saturday should further slightly stabilize but could still be triggered on previous lee slopes.
Snowpack Discussion
An atmospheric river and warm very wet weather was seen last week. About 5-8.5 inches of mostly rain was seen along the west slopes. This caused an avalanche cycle, consolidation and stabilizing of the older part of the snowpack along the west slopes and is expected to have eliminated persistent weak layers at Stevens and Snoqualmie.
A stormy pattern with cooling was seen late last week and over the weekend with about 1.5-4 feet of snowfall along the west slopes.
Reports varied on Sunday. The Mt Baker and Alpental ski areas reported widespread avalanches released from explosives ranging from 1-2 feet and running good distances, releasing on storm snow interfaces. The Stevens Pass ski area reported morning control produced widespread soft slab results from both explosive and ski cuts with best results on NW-SE facing terrain with slides releasing on the most recent storm interface with Friday's storm snow.
Across the street at Skyline Ridge at Stevens Pass NWAC observers found about 30-60 cm of mostly stable, mostly right side up storm snow, well bonded to Tuesday's rain crust. One 30-40 cm storm slab was triggered on a 40 degree slope which ran on the crust from early last week.
A cool day with little if any new snowfall on Monday will have brought some stabilizing.
Terrain anchors have been somewhat buried by recent snowfall but will still add significant anchoring below about 3500-4000 feet.
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, South.
Elevations: Alpine, Treeline.
Likelihood: Possible
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: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1