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Archived

Avalanche Forecast

Jan 6th, 2016–Jan 7th, 2016
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 - South East.

In specific areas, where the most recent storm snow is more cohesive, small human-triggered slab avalanches will be possible. Before committing to a slope, think about the consequences of the terrain if even a small avalanche occurred. New wind slab will most likely be found in the central and southeast zones near and above treeline.  

Detailed Forecast

In general, the most recent storm snow overlying recently buried weak layers is lacking widespread cohesion to be deemed likely to trigger. In specific areas, where the storm snow is more cohesive, small human-triggered slab avalanches will be possible. Before committing to a slope, think about the consequences of the terrain if even a small avalanche occurred. Note density changes in the upper snowpack throughout the day and as you change aspect and elevation.  

Moderate southerly winds for the central and southeast Cascades may have built new wind slabs over the last day or two in the near and above treeline zones. Look for signs of firmer wind transported snow that can indicate wind slab layers.

Snowpack Discussion

Fair weather was seen for almost a week around the New Year. This weather extensive consolidation and stabilizing of the snow from December. It also caused extensive surface hoar and near surface faceted snow on non-solar sheltered slopes according to reports for west and east of the crest in the Washington Cascades. Since Sunday, a few inches of steady light snow has accumulated along the east slopes, with up to 12 inches at Mission Ridge with only moderate SW ridge-top winds. 

Tom Curtis was west of Blewett Pass around Iron Mountain New Years Day and found the December 13 buried surface hoar layer 60 cm down that showed sudden collapses in several column tests, including PST with a firm slab overhead. In this area, the layer was prevalent on NE-E aspects around 5300 ft near treeline. This may be a layer of concern to track or look for moving forward in this specific area. 

PST End down 60cm on 20151213 buried surface hoar layer. West of Blewett Pass, January 1, 2016. ENE aspect NTL @ 5330ft. Photo: T. Curtis

The North Cascades Mountain Guides on January 1st and 2nd at Washington Pass generally report good stable conditions and a lack of results in snow pit tests. Minor wind effects have been noted near ridges.

Reports via the NWAC observations page for January 2nd at Blewett Pass, email received at the NWAC from Holden for January 3rd and further reports via the NWAC observations page for January 4th for Stevens and Snoqualmie help confirm the extent of the recently buried surface hoar.

Avalanche professionals in the Tumwater Canyon area Wednesday reported the 1/3 surface hoar layer about 20 cm down on a NW aspect at 4000 ft, but lacking the cohesiveness to present a slab problem. The surface hoar layer was also found on solar aspects at this elevation. 

 

Avalanche Problems

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

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, South East, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1