Avalanche Forecast
Regions: Snoqualmie Pass.
Sunday should be fairly stormy day west of the crest. New storm and wind slab layers are likely.
Detailed Forecast
A wet cold front will cross the Northwest Saturday night. Snow levels will be highest on Saturday night. A good period of southwest-west flow, moderate to heavy orographic snow showers, and cooling with lowering snow levels should be seen on Sunday. New snow by the end of the day Sunday west of the crest should vary a lot from lower to higher elevations with a foot or more at higher elevations.
Building storm slab is likely mainly near and above treeline on Sunday. Watch for cracking and releases on steep sheltered slopes where snowfall exceeds an inch an hour for more than a few hours.
Building wind slab is also likely mainly near and above treeline on Sunday. Watch for firmer wind transported snow on lee slopes.
The freezing rain crust at Snoqualmie may act as a bed surface in that area.
The cooling should cause some good snow conditions on other slopes. Don't let powder starvation change plans to stick to safe slopes on Sunday. It is always a good plan to give new snow layers a day to stabilize before venturing to steeper slopes after a storm.
Snowpack Discussion
A front late Thursday was followed by showers Friday. West of the crest this gave up to about 10 inches of storm snow.
Some natural storm slab avalanches were reported in the Mt Baker backcountry. The avalanches released on north aspects at 5000 feet, about size R2, small relative to paths.
NWAC observer Dallas Glass and the Alpental patrol report a freezing rain crust on the surface at Snoqualmie on Thursday and Friday which may act as a bed surface in that area Sunday.
The underlying mid and lower snowpack west of the crest mainly consists of melt-freeze crusts and stabilized rounded grain layers. This is due in great part to the warm and dry period from about 6-15 January and previous similar 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
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.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1