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Archived

Avalanche Forecast

Feb 2nd, 2015–Feb 3rd, 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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Cascades - North West.

Storm and wind slabs remain possible Tuesday, especially on lee aspects near and above treeline. Watch for wind transported new snow received Sunday and Monday, especially higher terrain. 

Detailed Forecast

Little or no precipitation is expected early Tuesday, with light rain and snow increasing in the afternoon along the west slopes. 

Shallow storm slabs formed Sunday and Monday may be poorly bonded to old surface crusts, especially near and above treeline on lee aspects. 

Snowpack Discussion

The weekend of Jan 24-25th, a warm and wet weather system caused high snow levels and rain and allowed for extensive snowpack settlement. Last week, high pressure aloft caused abundant sunshine and mild temperatures. A frontal system crossed the PNW on Sunday, producing generally light amounts of new snow, except moderate amounts in the Mt. Baker area above 4-4500 feet. Another but weaker front moved across the region Monday. Moderate S - SW winds built new shallow wind slab near and above treeline in the Mt. Baker zone near Artist Point as reported by NWAC observer Jeff Hambleton on Monday, February 2. The winds had redistributed the storm snow, which ranged from 0 to about 10 inches depending upon terrain with wind affects noted and cross loading as well. Under the recent storm snow the strong crust was about 10 inches thick and stability tests indicated a fairly good bond existed. Some shallow failures were noted in the upper few inches of storm snow and just above the crust with little to no propagation observed.     

Prior to the recent frontal systems, the snowpack was dominated by strong surface crusts, limiting the avalanche potential. There had been surface hoar growth noted last week on shaded terrain mainly below about 5000 feet, along with some near surface faceting (NSF) on non-solar slopes. Surface hoar/NSF may have been buried by the light snowfall and initial cool temperatures Sunday. Warning and some rain may have subsequently destroyed this in the BTL band however, where little new snow accumulated as of Monday. 

See Jeff Ward's video from the Steven's Pass area below.

The snowpack west of the crest mainly consists of the generally shallow recent storm snow over 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, North East, East, North West.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 1

Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1