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Avalanche Forecast

Archived

Feb 25th, 2017–Feb 26th, 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 generally shallow new wind slab on lee easterly aspects. Fresh wind slab should mainly be found near and above treeline. Fast moving loose dry avalanches are possible on steeper slopes in non-wind affected terrain.

Detailed Forecast

A low pressure system moving south along the Washington Coast on Sunday should produce light amounts of low density snow along the east slopes of the Cascades. 

While older wind slab continues to exist on isolated lee slopes mainly above treeline, we will shift our focus to new wind slab formed Saturday afternoon through Sunday morning. Existing weak surface snow in addition to new low density snowfall will be transported to lee slopes mainly near and above treeline. Watch for generally shallow new wind slab on lee easterly aspects. Fresh wind slab should mainly be found near and above treeline.   

Watch for loose dry avalanches on steeper slopes in non-wind affected terrain. Be especially wary of fast running loose dry avalanches near terrain traps. 

Give cornices a wide berth when traveling along ridgelines and avoid lingering on slopes below cornices as they may fail at any time.

Snowpack Discussion

Weather and Snowpack

In the northeast zone the NWAC station at Washington Pass received about 10-14 inches of moist snow over a thin freezing-rain crust formed early in the Valentine's Day storm cycle. In the central-east and southeast zones, light rain likely formed a crust up to 5-6000 feet in the central-east and up to about 7000 feet in the southeast zone. A short period of fair weather on Friday, 2/17 caused another surface crust, especially on solar aspects.

A slightly unstable weather pattern this week caused a mix of sun and light snow showers with cold temperatures and light winds from Tuesday through Friday. The weather this week helped to freshen the surface with up to several inches of snow while sun crusts formed on solar aspects.

Saturday started off mostly sunny but high clouds increased in the afternoon. Increasing westerly ridgetop winds were noted at Mission Ridge and Dirty Face Peak on Saturday afternoon ahead of a frontal system. 

Recent Observations

North

Recent reports around the Washington Pass area over the past few days including Saturday 2/25, continue to indicate excellent quality snow conditions. The only avalanche problem on Saturday were small fresh wind slabs forming in isolated areas above treeline on lee slopes. 

Central

Tom Curtis was in the Blewett Pass area Wednesday 2/22 and found the recent wind slabs were confined to very isolated terrain features on mostly easterly facing terrain at higher elevations. These slabs remained sensitive to ski trigger, but were very isolated in extent, ranging from 2-8 inches.

Very similar conditions were reported from Mission Ridge Wednesday 2/23, with isolated wind slabs of 6-8 inches confined to specific steep terrain features below ridges.  

South

No recent observations. 

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 Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These 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.