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Archived

Avalanche Forecast

Feb 27th, 2015–Feb 28th, 2015
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
1: Low
The avalanche danger rating in the alpine will be low
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Cascades - West.

Shallow wind slabs may have formed Friday night and Saturday morning mainly on westerly aspects near and above treeline. 

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. 

After some light snow accumulations midweek along the west slopes midweek, 6-10 inches of new snow accumulated Thursday night and Friday above 4000 ft from Snoqualmie Pass and south, including Crystal Mt and Mt. Rainier. Generally an inch or less was received further north.  

Professional NWAC observer Jeremy Allyn was at Paradise on Friday and found 25 cm (10 in.)  of new snow bonding well to previous snowfall received midweek and layering with a favorable density profile. By mid-day Friday, east winds were beginning significant snow transport near treeline and fresh wind slabs were developing on westerly aspects as evidenced in this short video clip from Jeremy on our Instagram account. 

The mid and lower snowpack west of the crest snow consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

Avalanche 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: Possible

Expected Size: 1 - 1