Avalanche Forecast
Issued: Jan 2nd, 2016 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Watch for isolated areas of wind slab primarily on north through southeast aspects above treeline and for terrain traps on steeper slopes throughout the terrain.
Summary
Detailed Forecast
The recent clear weather should give way to increasing clouds and a return to a few light showers, especially late Sunday at still cool temperatures. The areas near the crest, east of the passes and approaches to the passes will remain cool.
This weather will continue to allow the 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 since Thursday and will likely not have built new wind slab on westerly aspects. Watch and test for inverted strong over weak storm snow.
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. In this area, the 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 may be a layer of concern to track or look for moving forward in this 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
Valid until: Jan 3rd, 2016 10:00AM
