Avalanche Forecast

Issued: Feb 10th, 2018 10:00AM

The alpine rating is moderate, the treeline rating is low, and the below treeline rating is low. Known problems include Wind Slabs.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Avoid wind deposited snow above treeline where you will be able to trigger an avalanche. Wind sculpted features, cornices, and stiff snow drifts all indicate Wind Slabs have formed in the terrain.

Summary

Detailed Forecast

Wind Slabs will linger above treeline Sunday especially around Washington Pass. You will be most likely to trigger these avalanches on steep lee slopes and cross-loaded terrain features. Identify and avoid areas where wind deposited snow such as near wind sculpted features, below cornices, or on wind drifts. Very strong and gusty winds have formed Wind Slabs on a variety of slopes including areas you do not normally see them.

Loose surface snow exists on sheltered slopes. Expect small Loose Dry avalanche in steep terrain. Some of these small avalanches may run far and fast. Avoid steep slopes above cliffs, rocks, and gullies where even small avalanches may have higher consequence.

Cornices have grown very large throughout the recent stormy period. Cornice fall is very unpredictable. Limit your exposure as much as possible if you must travel them.

Other non avalanche hazards exist in the mountains. Firm icy slopes will make stopping a fall very difficult. Avoid traveling on steep terrain if you encounter this potentially dangerous surface condition.

Snowpack Discussion

Westerly winds formed small isolated wind slabs above treeline this past week. In areas around Washington Pass 3-7 inches of snow sits on top of the most recent crust near and above treeline. Significantly less snow fell in areas east and south.

Warm weather in early February has created a strong and consolidated mid and lower snowpack in most areas. Unstable snow has been limited to shallow surface layers.

In the last week of January observers reported isolated buried surface hoar on top of the 1/16 crust. This persistent weak layer was found or thought to be the cause of several avalanches. Though it’s no longer a main concern, use caution when traveling in areas further east of the crest where this layer may survive. Snow profiles and snowpack tests are the best means to confirm the presence of this layer.

Observations

North

On Saturday 2/10, avalanche professionals in the Washington Pass area reported winds slabs continuing to gain strength. The sun affected surface snow conditions on South aspects by later in the day. 

On Friday 2/9, avalanche professionals near Washington Pass triggered a small slab avalanche above treeline. Small loose dry avalanches in steep terrain were also observed.

Central

No recent observations have been received.

Problems

Wind Slabs

An icon showing 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: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Feb 11th, 2018 10:00AM