Avalanche Forecast
Issued: Feb 14th, 2018 10:12AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Use visual clues such as blowing snow, fresh cornices, snow drifts, and variable snow surfaces with cracking to identify and avoid wind slabs above treeline. The new storm snow is poorly bonded to the old snow surface. You may trigger small loose dry avalanches until this bond improves.
Summary
Detailed Forecast
Small wind slabs will be found on lee slopes above treeline Thursday. Identify and avoid wind deposited snow below ridgelines. Blowing snow, fresh cornices, and snow drifts all indicate that wind slabs are present in nearby terrain. Use visual clues to help you identify wind slabs and select safer travel routes.
The new snow is poorly bonded to the old snow surface. Small loose dry avalanches will still be possible until this bond improves. Avoid steep slopes above terrain where even a small avalanche may have large consequences such as above cliffs, rocks, and open creeks.
In some locations snow fell on a firm icy surface crust. Be careful if traveling on steep firm slopes where stopping a fall will be very difficult.
Snowpack Discussion
A few inches of new snow fell around the east slopes of the Cascades Wednesday. In exposed areas above treeline, winds drifted snow forming small shallow wind slabs on lee slopes. New storm snow bonded poorly to old snow surfaces. A wide variety of old surfaces include melt-freeze crust on sun exposed slopes, weak surface facets and surface hoar in sheltered areas, and wind textured snow on exposed features.
Below the old snow surface a relatively well consolidated snowpack exists. While we are tracking several older crust layers there are currently no significant layers of concern in the snowpack.
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. A recent observation (2/11) from the Mission Ridge area confirmed this layer is still present in some locations. Although it is 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
Over the last several days, avalanche professionals in the Washington Pass area reported no new avalanche activity with debris from the most recent 2/5 avalanche cycle visible in many paths. Recent winds have created a variety of snow surface conditions above treeline. On Sunday, observations from professionals near Hart's Pass noted surface hoar up to 1 cm thick on all aspects up to a few hundred feet below ridgecrest.
Central
A recent observation from the Mission Ridge/Lake Clara area.
Problems
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
Expected Size
Valid until: Feb 15th, 2018 10:12AM
