Avalanche Forecast
Regions: Snoqualmie Pass.
Very dangerous avalanche conditions are expected Sunday night and Monday and travel in avalanche terrain is not recommended.
Detailed Forecast
Moderate snow is forecast to change to rain Sunday night. Moderate to heavy rain should reach up into the above treeline elevation band through Monday. This will orient the avalanche type toward wet slab and wet loose. Heavy rain should quickly load snowfall received earlier in the storm and result in widespread natural loose wet avalanches especially in steeper terrain. Natural wet slabs have the potential to be larger and more destructive while less predictable. With the strong winds forecast... there should be new wind slab in the upper part of the above treeline elevation band. The avalanche danger may be locally lower in areas that receive less snow and rainfall, such as the Crystal Mt. area.Â
Due to the significant warming and precipitation Sunday night and Monday, a natural avalanche cycle is expected and an avalanche warning has been issued.  Backcountry travel in avalanche terrain is not recommended Monday.Â
Snowpack Discussion
Avalanche concerns along the west slopes of the Cascades are becoming all storm related. On Sunday snow accumulated with rising temperatures leading to inverted new snow layering. The winds also increased during the day Sunday, transporting new snowfall to lee aspects. Mt. Baker pro-patrol reported easy ski triggering of 6-10" soft wind slabs around mid-day.Â
Besides the expected storm snow instabilities, direct-action avalanches may step down to a variety of older snow surfaces; near surface facets, wind board, melt-freeze crusts, etc. Also of concern will be a thin layer of surface hoar formed midweek in sheltered areas below tree-line. In the Stevens Pass zone, WSDOT avalanche forecaster Brandon Levy found areas of 4 mm surface hoar buried intact around Stevens Pass Saturday morning. Â
A generally strong mid and lower snowpack is expected west of the crest. One caveat is a persistent weak layer noted near a crust about 1 meter down in the Stevens Pass area last week, but no known avalanche activity has occurred on this layer.
Avalanche Problems
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 2
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very 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: Alpine.
Likelihood: Likely
Expected Size: 1 - 2