Avalanche Forecast
Regions: Snoqualmie Pass.
The avalanche danger west of the crest should gradually decrease on Monday. Watch for lingering wind and storm slab especially above treeline.
Detailed Forecast
Light west flow, light snow showers mainly west of the crest and slightly lower snow levels should be seen on Monday. This should not build significant new layers. The avalanche danger should gradually decrease on Monday as new layers from Sunday partly stabilize.
Wind slab from Sunday should linger west of the crest mainly above treeline on Monday. It is also possible near treeline depending on if there is significant snowfall in this band on Sunday. Watch for firmer wind transported snow on previous lee slopes.
Storm slab from Sunday may linger to some extent west of the crest on Monday but will be stabilizing. Watch for cracking and releases on steep sheltered slopes where snowfall exceeded an inch an hour for more than a few hours on Sunday.
The cooling should cause some good right side up snow conditions on other slopes on Monday.
Snowpack Discussion
Strong southwest flow carried a wet front across the Olympics and Cascades Saturday night. This front tapped subtropical moisture so snow levels got pretty high with 2-3 inches of rain at most NWAC sites west of the crest. A big exception was Stevens Pass with 15 inches of snow overnight.
West southwest flow and mostly moderate to heavy orographic showers are occurring Sunday with slightly lowering snow levels.
A couple of reports are on hand for Saturday night and Sunday. The Stevens Pass ski patrol reported there were many small natural storm slab avalanches with crowns of about 10 inches Saturday night. A ski patroller triggered a R2D2 of about 6-10 inches within the ski area on Sunday.
NWAC observer Dallas Glass is at Paradise on Sunday. He reports only about 2-4 cm of new snow so far but that strong winds are beginning to create wind slab in the near and above treeline.
Under the surface mid and lower snowpack layers west of the crest mainly consist of melt-freeze crusts and stabilized rounded grain layers from warm periods so far this winter. Persistent weak layers are not expected west of the crest.
The overall snowpack remains well below normal for this time of year and some windward or southerly aspects have little if any snow cover.
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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.
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