Avalanche Forecast
Regions: Snoqualmie Pass.
New wind slab should be found on a variety of aspects Monday, mainly near and above treeline. Remember MODERATE danger means human triggered avalanches are possible. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees.
Detailed Forecast
Wind slab will most likely be found on north to southeast aspects near and above tree line, except locally on west-northwest aspects near the Cascade Passes. NW winds will redistribute new snowfall to lee SE slopes above treeline Monday. Wind and storm slab avalanches should stay within recent storm layers. Test for inverted strong over weak storm snow and give cornices a wide margin.
Beware of loose dry avalanches in steep non-wind affected terrain that could have unintended consequences such as knocking you off your feet and into a terrain trap.
There have been snow immersion fatalities in tree wells already this season at Snoqualmie and in Canada. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees and maintain visual contact. Â
Snowpack Discussion
For the week ending on Dec. 24th, a snowy and cool storm cycle brought 5-9 feet of snowfall along the west slopes. Only light additional accumulations over the last few days have allowed the snowpack to gradually settle, but it remains deep out there with generally great skiing and riding! Â
The upper snowpack should generally be right side up with increasing hardness with depth. Moderate S-SW transport winds with Sunday's system may have built new wind slab on N through E aspects. However, Alpental pro-patrol did observe local east winds at Snoqualmie Pass building thin wind slabs over weaker snow near treeline Sunday. Â
The most recent snowpack and avalanche observations include shallow storm slab releases from Alpental pro-patrol during AM control work on Christmas and of a small skier triggered storm slab near treeline in the Crystal backcountry Saturday. Light snowfall on Sunday was not expected to significantly increase the storm hazard.
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, West, North West.
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1