Avalanche Forecast

Archived

Dec 3rd, 2017–Dec 4th, 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, human triggered possible.

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

Sunny weather should be seen on Monday with light northwest winds and recent snow layers will continue to stabilize.

Wind slab is replacing storm slab as our primary avalanche problem as storm snow will be stabilizing and increasingly less likely to trigger.

Small wind slabs should remain generally on NW through E aspects on Monday and should become more stubborn or difficult to trigger. Watch for areas of firmer, wind-transported snow mainly on lee terrain features.

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 past week at all stations in the Cascades since the Thanksgiving warm period: Locations on the east side of the Cascade crest have received 5-15".

Recent snow accumulation for the 48 hours ending on December 3 along the Cascade east slopes have been light, ranging from 1-8".

Since about Monday November 27th, temperatures have generally been steady in the upper teen's to mid twenties and winds at higher elevations have generally been WSW in the single digits to the low twenty mph range.

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 reactive 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.

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.