Avalanche Forecast
Issued: Jan 1st, 2016 11:09AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Dry.
NWAC,
Northwest Avalanche Center
Watch for isolated areas of wind slab primarily on north through southeast aspects above treeline and for small loose avalanches near terrain traps on steeper slopes throughout the terrain.
Summary
Detailed Forecast
High pressure will bring more sunny weather to higher elevations while low level clouds and valley fog will linger along the east slopes Saturday.
This weather will continue to allow older wind slab to slowly settle and stabilize. Wind slab will most likely be found on north to southeast aspects near and above tree line. Any wind slab avalanches should be confined to surface layers and cool temperatures east of the crest will slow the stabilizing of these layers. East winds were much lighter east of the crest Thursday and Friday and will likely not have built new wind slab on westerly aspects. Watch and test for inverted strong over weak storm snow.
The sunny weather should bring the possibility of loose avalanches Saturday afternoon on steep slopes. Small loose avalanches could be skier triggered on any steep aspect, or potentially by the sun on solar aspects, either way be aware of terrain traps where even a small avalanche could have big consequences.
Snowpack Discussion
A cool and snowy storm cycle brought 2-4 feet of snowfall to the east slopes the week ending December 24th. Light additional accumulations over the past week have allowed the snowpack to slowly settle and good skiing and riding conditions have been reported in non-wind affected terrain.
Recently, separate observations from NWAC observer Tom Curtis in the Blewett Pass backcountry and Icicle Canyon area as well as North Cascades Mountain Guides report generally a right-side up snowpack in non-wind affected terrain with widespread surface hoar and near surface faceting in sheltered areas in all elevation bands. Isolated pockets of wind slab are still thought to exist in the above treeline zone. Loose dry avalanches are still possible on steeper slopes, whether potentially triggered by skiers or on solar slopes by sunshine.
Tom was west of Blewett Pass at Iron Mountain Friday and found a buried surface hoar layer 60 cm down that showed sudden collapses in column tests with a firm slab overhead. This layer was prevalent on NE-E aspects around 5300 ft near treeline. There were not any recent skier or natural triggered avalanches on this layer, but it is a layer of concern to track moving forward in this very specific area.
The southeast zone has a shallower snowpack versus areas further north, but after a snowy few weeks, has more than enough snow to warrant an avalanche risk. No snowpack observations have been received from this 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, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Dry
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose Dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose Dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Loose Dry avalanche with the characteristic point initiation and fan shape.
Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 2nd, 2016 11:09AM
