Avalanche Forecast
Regions: Cascades - South West.
Watch for new wind slab on lee slopes near and above treeline. Loose sluffs should be manageable except be wary on steeper slopes near terrain traps.
Detailed Forecast
Isolated snow showers, sun breaks, light NW winds and cool temperatures should do little to change the avalanche danger Christmas Day. Watch for new wind slab on lee slopes near and above treeline. NW winds may have loaded southeasterly aspects more than usual. Loose sluffs should be manageable except be wary on steeper slopes near terrain traps.Â
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Snowpack Discussion
A warm and moist storm system over the weekend brought heavy snow changing to rain and then back to snow along the west slopes. A natural avalanche cycle likely peaked Saturday night during the height of the warming. Deeper instabilities were noted in the Mt. Baker and Crystal Mt area where the storm snow initially bonded poorly to weaker snow above the old rain crust.Â
The frontal system that impacted the area Tuesday through Wednesday morning started warm and ended cold for a right side up layering. New snowfall generally ranged 6-12", with lower amounts near Snoqualmie. Â Winds turned northwesterly with the cool-down... loading SE aspects Wednesday.Â
Crystal mountain pro-patrol saw little in the way of control results Wednesday morning. NWAC Pro-observer Jeff Hambelton in Mt. Baker area found a right-side upper snowpack. Moderate wind transport had created a stiffer layer of snow on some lee slopes near and above treeline and observed small loose dry sluffs - Watch Jeff's video. Â
The lower snowpack is generally strong and comprised of crusts and polycrystals. Â
If traveling to the east slopes of the Cascades be aware their different snowpack structure containing persistent weak layers and read the avalanche forecast.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, South.
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