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Archived

Avalanche Forecast

Mar 1st, 2015–Mar 2nd, 2015
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Some strong N-NE winds later Monday may transport any available surface snow to more unconventional southerly facing slopes. 

Detailed Forecast

Clearing skies, cool temperatures and increasing northerly crest level winds are expected Monday. Watch for new shallow wind transport to more southerly facing slopes, especially near and above treeline where stronger winds are expected. 

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

A warm and wet start to February, was followed by mostly fair weather through mid-February, leading 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. Much less new snow was received from Stevens Pass to Mt Baker, where only an inch or so fell.  

Professional NWAC observer Jeremy Allyn was at Paradise last 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 this video clip attests. 

Gusty and strong E-NE winds were visibly seen transporting surface snow on the Mt Rainier camera Saturday, mostly at higher elevations, though the east sides of trees were void of snow near treeline confirming the winds earlier affects.  

Early March sunshine contributing to warm daytime temperatures Sunday has likely settled recent wind slabs. 

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: South, South West, West, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1