Avalanche Forecast

You will be able to trigger avalanches Thursday in a variety of locations along the eastern region of the Cascades.

Moderate to strong S and SE winds transported fresh snowfall to create new and reactive wind slabs Wednesday night on lee slopes near and above treeline. These new wind slabs overlay older and deeper wind slabs formed Sunday. Visual clues such as wind drifted snow, a lack of snow in the trees, and surface cracking can indicated wind slabs have formed on nearby slopes. Identify and avoid all slopes over 35 degrees where the winds deposited snow.

Several old weak layers exist in the snowpack around the east side of the Cascades. The exact layer and depth depend on aspect, elevation, and proximity to the Cascade crest. A high level of uncertainty remains surrounding these layers. Snow profiles and snowpack tests can confirm the presence of a weak layer but cannot prove its absence. Continue to be cautious and stay away from large open slopes where you could trigger a Persistent Slab avalanche. A resulting avalanche will likely be large and could kill you. If you experience collapsing or audible whumphs, stay away from any nearby avalanche terrain.

A few inches of new snow was seen around the eastern Cascades by Wednesday afternoon. This fresh snow has fallen on a variety of snow surfaces including thin sun crust, uneven wind surfaces, and soft unconsolidated snow. Moist snow surfaces and roller balls may be found at lower elevations.

A number of potential persistent weak layers exist in the snowpack around the eastern Cascades. Two common layers that have been reported in many locations are a facet/crust combination buried on 2/23 and a facet/crust layer buried on 2/13.

The upper (shallower 2/23) layer can be found 6-14” below the snow surface on steeper slopes that have received direct sun. Small weak facets have been found in other regions surrounding a thin sun crust formed early last week and buried during last weekend’s storms.

The deeper (2/13) facet/crust combination is typically found 2-3 feet below the snow surface. This layer has been around for two weeks with two confirmed skier triggered avalanches and more recent collapsing and whumphing. With significant new snow added to the snowpack last weekend, this layer may be reactive in areas where we have not seen previous avalanche activity nor snowpack test results. These weak sugary facets are located above a firm wide spread crust buried on Feb 5th.

While several layers exist in the snowpack, there are no significant layers of concern below the 2/5 crust.

Observations

North

On Tuesday and Wednesday, avalanche professionals near Washington Pass observed small wind slabs near ridgeline and localized cracking. Moderate, gusty winds were transporting snow.

On Monday, the crown of a large avalanche was visible on Scaffold Ridge (Twisp River) in the North Cascades. Interestingly the red line in the photo marked the initial crown width that released Sunday and the remainder of the slab released sometime later Monday morning.

The most recent persistent slab avalanche occurred on February 21st near Harts Pass. The avalanche was about two feet deep and 90 feet wide. It occurred on a NE aspect at 6000’.

Large natural slab avalanche visible on Scaffold Ridge in the North Cascades, starting zone about 7300'. Image, Matt Firth  

Central

On Wednesday, An avalanche professional in the Chiwakum Mountains reported collapses and whumps on the 2/13 buried facet layer. Depth to the layer was highly variable (1-3 feet). 

Another avalanche professional in the Chiwaukum mountains traveled in a low-elevation terrain on a N-NW aspect and found the 2" thick 2/13 buried facet layer well preserved and 16" down. He also observed moist surface snow conditions up to 3400 feet with lots of roller balls.