Avalanche Forecast
Issued: Feb 27th, 2015 10:29AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Shallow wind slabs may have formed Friday through Saturday morning mainly on westerly aspects near and above treeline.
Summary
Detailed Forecast
Moderate east winds will become northeasterly Friday night and continue loading westerly aspects through mid-day Saturday.
Shallow winds slabs may be possible Saturday and generally found on non-traditional westerly aspects near and above treeline. Pay attention to how much if any new snow was received in the area you're traveling and may have been available for transport.
Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow (new or existing) to pose an avalanche hazard.
Snowpack Discussion
Since the warm and wet start to February, fair weather through mid-February has led to generally thick surface crusts, as well as further deterioration of the snow cover below treeline.
6 inches of new snow accumulated Thursday night and Friday at the NWAC mid-station at Mission Ridge. These new snowfall amounts were likely representative of most of east slope locations above 4000 ft except in the northeast Cascades where only an inch or two of new snow likely accumulated. By early Friday, east winds were beginning significant snow transport near treeline and fresh wind slabs were likely developing on westerly aspects.
While the January 15th facet/crust layers can still be identified in parts of the NE Cascades, this persistent weak layer has been stabilizing and become unlikely to trigger. As a result the Persistent Slab problem has been removed from the northeast zone.
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: North, South, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 28th, 2015 10:29AM
