Avalanche Forecast

Archived

Dec 2nd, 2017–Dec 3rd, 2017

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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Fresh wind slabs should be touchy Saturday and generally found near and above treeline. Approach ridges cautiously and watch for firmer wind-transported snow. Storm slabs should be shallow but may exist in specific areas throughout the terrain. Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Detailed Forecast

Generally light and isolated showers Saturday morning should transition to more widespread shower activity in the afternoon. Showers are expected to be heaviest in the late afternoon and evening with some upslope enhancement for the east slopes of the Cascades. See the NWAC mountain weather forecast tab for more details.

Fresh wind slabs should be touchy Saturday and generally found near and above treeline. Approach ridges cautiously and watch for firmer wind-transported snow.

Storm slabs should be shallow but may exist in specific areas throughout the terrain.

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Snowpack Discussion

Warm, wet weather before Thanksgiving caused first storm then wet snow avalanches in the Washington Pass area. Post-Thanksgiving about 2 feet of snow has accumulated in the Washington Pass area. There is now about 1-2 feet (30-60 cm) above the Thanksgiving Day crust in the Washington Pass area.

Outside of the Washington Pass area, less recent snow has accumulated for the central-east and southeast Cascades during the week. Snow depths are limited in these areas.

Observations

North

None

Central and South

None

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.