Avalanche Forecast
Regions: Snoqualmie Pass.
New wind and storm slab should be the main avalanche problems on Sunday. A surface hoar layer from Thursday night will increase instability where it gets buried intact.
Detailed Forecast
Decreasing northwest winds, decreasing light snow showers and a cooling trend should be the main story near and west of the crest on Sunday. New snow should run in the 7-15 inch range near and west of the crest.
The main avalanche problems Sunday should be new storm and wind slab. Storm slab will occur in areas that receive more than an inch of snow an hour for several or more hours. For wind slab watch for firmer wind transported snow on lee slopes.Â
The surface hoar will increase instability where it gets buried intact. You can check for this layer using hand shear tests or shovel tilt tests.
A trend of decreasing danger should be seen on Sunday as new layers begin to stabilize. The trend of decreasing winds, decreasing light showers and cooling should also cause some nice right side up conditions on some sheltered slopes.
Snowpack Discussion
A warm storm moved over the Northwest Tuesday and Wednesday with strong west winds followed by lowering snow levels. About 3-12 inches of snow was seen at NWAC sites near and west of the crest at the tail end of the storm.
A cooler period with little precipitation was seen about Thursday to Friday. Some skiers were reporting better conditions on lower angle slopes with skis scraping crusts on some steeper slopes.
NWAC observer Dallas Glass was touring above Paradise Friday and found about 10 inches of recent storm snow well bonded to a firm rain crust. The lower snowpack was generally composed of stable crusts and polycrystals. He saw widespread 5 mm surface hoar which had formed Thursday night.
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Sparkly surface hoar on a SW aspect at 6000 feet at Paradise Friday by Dallas Glass.
 A cold front is moving over the Northwest on Saturday and Saturday night causing west winds and moderate to heavy snow and snow showers near and west of the crest and a cooling trend. This should build some new wind and storm slab by Sunday.
Avalanche Problems
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: Likely
Expected Size: 1 - 1
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: Likely
Expected Size: 1 - 1