Avalanche Forecast

Archived

Feb 26th, 2017–Feb 27th, 2017

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

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 mainly above treeline. Fast moving loose dry avalanches are possible on steep slopes in non-wind affected terrain.

Detailed Forecast

A weak low pressure system moving south along the Washington Coast on Monday should produce light snow showers, mainly in the afternoon, and mainly for the central-east and southeast Cascades near the Cascade crest.

Watch for generally shallow new wind slab formed Saturday on lee easterly aspects. Fresh wind slab should be found mainly above treeline. Be aware that lower density snowfall received as the winds eased Sunday may obscure recently wind loaded slopes.

Watch for loose dry avalanches on steep 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

The most recent atmospheric river arrived on Valentines Day 2/14 and formed the uppermost significant rain crust in our snowpack for the central-east and southeast Cascades with only a thin freezing rain crust seen in the Washington Pass area. A slightly unstable weather pattern last week caused a mix of sun and light snow showers with sun crusts forming on solar aspects.

Saturday started off mostly sunny but high clouds increased in the afternoon. Increasing westerly ridgetop winds were noted at the Mission Ridge and Dirty Face Peak weather stations and by NCH on Saturday afternoon in the Washington Pass area. Light snow showers produced an inch or three of low density snowfall along the east slopes of the Cascades on Sunday with generally light winds.

Recent Observations

North

Recent reports around the Washington Pass area from NCH and NCMG over the past few days continue to indicate excellent quality snow conditions. The primary avalanche problem noted was shallow wind slab formed Saturday in isolated areas above treeline due to moderate W-NW alpine winds.

A public observation received via the NWAC observation page Saturday indicated a small natural loose dry avalanche, possibly cornice triggered, that hit a skier on the Silver Star glacier.

Central

No recent observations.

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.