Avalanche Forecast

Archived

Jan 4th, 2015–Jan 5th, 2015

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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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.

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.

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.

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.

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.

Problems

Wet Slabs

Wet Slab avalanches are the 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 Slabs can be very unpredictable and destructive.

Loose Wet

Loose Wet avalanches are the 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. 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.

Wind Slabs

Wind Slab avalanches are the 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.