Avalanche Forecast

Archived

Feb 23rd, 2018–Feb 24th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

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You will be able to trigger wind slab avalanches in wind loaded terrain near and above treeline. Use visual clues to identify and avoid slopes where winds have deposited snow. The persistent slab problem still exists. Stay off of large open slopes greater than 35 degrees where you may trigger this difficult to manage avalanche problem.

Detailed Forecast

Avoid steep wind loaded slopes near and above treeline Saturday where you will be able to trigger wind slab avalanches. Use visual clues such as fresh cornices, snow drifts, and uneven surface snow with cracking to identify slopes where winds have deposited snow. Wind slabs may form along ridgelines and cross-loaded mid-slope features.

A persistent slab problem will continue Saturday in the Mt Baker area. Conditions this past week have not allowed this dangerous weak layer to sufficiently heal. A higher degree of spatial variability exists on this layer in the Baker area. However, it can be very difficult to determine exactly where this layer is and is not present. Snow profiles and snowpack tests can confirm the presence of this layer but cannot prove its absence. Continue to stay off of large steep open slopes where you may trigger this avalanche.

Good travel conditions can be found in sheltered terrain on slopes less than 30 degrees away from overhead hazard.

Snowpack Discussion

Moderate to strong winds Friday afternoon began to transport loose surface snow forming new wind slabs on lee aspects. The upper snowpack consists of 2-4 feet of soft settled snow. In some locations this snow sits on top of weak sugary facets. These facets can be located just above the most recent (2/8) crust layer. Several avalanches, collapses, and whumphs have been triggered on this persistent weak layer in other areas of the west slopes of the Cascades. Snowpack tests and observations from around the west slopes of the Cascades continue to demonstrate that this layer can fail and produce avalanches.

A high degree of spatial variability exists in the Mt Baker area where the facet layer has been found but is more localized.

Below the 2/8 crust there are no significant layers of concern.

Observations

North

Professional observations from the Mt Baker area report a high degree of spatial variability in the location of the weak facet layer.

Problems

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.