Avalanche Forecast

Archived

Dec 5th, 2017–Dec 6th, 2017

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

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Watch for mostly small wind-loaded pockets on steeper terrain, particularly above treeline and especially in the northeast zone. Approach ridges cautiously and watch for firmer wind-transported snow.

Detailed Forecast

Continued sunny and mild weather is expected Wednesday with some moderate to strong crest level easterly winds.

This should allow for further settlement of the recent storm layers and cause an overall slowly decreasing danger.

Small wind slabs may exist on a variety of aspects, mainly on exposed lee slopes receiving any transported snow. The warming surface snow should limit or end further transport. Any remaining wind slabs are expected to be stubborn or difficult to trigger. Watch for small areas of firmer, wind-transported snow on isolated, lee terrain features.

Continue to watch for isolated, small, loose wet avalanches on steep sun exposed terrain during the late morning or afternoon, especially on unsupported slopes or near rocks.

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 accumulated in the Washington Pass area and this amount has settled above the Thanksgiving Day crust.

A series of frontal systems produced snow over the week following Thanksgiving at all stations in the Cascades: Locations on the east side of the Cascade crest have received 5-15".

The most recent snowfall ended early Sunday. The 48 hour snow accumulation ending on Sunday, December 3 along the Cascade east slopes have been light, ranged from 1-8".

Dry and cool conditions Sunday and Monday have allowed for 1-3 inches of snowpack settlement and allowed recent storm layers to begin stabilizing.

Warm and sunny weather Tuesday allowed for further consolidation and some moist surface snow on solar aspects.

Observations

North

NWAC pro observer Jeff Ward was near Washington Pass on Tuesday and found 30-50 cm of low density snow on the Thanksgiving crust. Some small loose dry avalanches were triggered late in the day. There was evidence of buried wind slab, but the layers were not reacting to ski tests.

Central and South

On Saturday, backcountry professionals skiing at Ingalls Peak reported generally stable conditions with some small, unreactive wind slab.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.