Avalanche Forecast
Regions: Cascades - North East.
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.
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 New Year's Day. Cool temperatures will moderate somewhat on Friday, particularly in the alpine and in the northeast Cascades.Â
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 will likely not have built new wind slab on westerly aspects. Watch and test for inverted strong over weak storm snow.
The sunny weather and warmer temperatures at higher elevations mainly in the northeast Cascades should bring the possibility of loose avalanches Friday 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.
An observation posted to the NWAC observations Sunday described a shallow triggered wind slab on a SSE facing slope at 4500 feet, well below treeline, on a wind loaded feature near Merritt Lake off Highway 2.
More 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. Â
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.Â
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, South East.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
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: Possible
Expected Size: 1 - 1