Avalanche Forecast

Archived

Feb 28th, 2017–Mar 1st, 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, human triggered possible.

Regions

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Watch for fresh shallow wind slabs, mainly near ridges or cross loaded features near and above treeline. Fast moving loose-dry avalanches continue to be a problem in many areas, especially in steep terrain of consequence.

Detailed Forecast

A break between disturbances is expected during the day Tuesday before the next weather system arrives Tuesday afternoon. Cold temperatures, light winds and increasing light snow showers by late Tuesday afternoon, should not appreciably change the current avalanche danger.

Watch for fresh, generally shallow wind slabs on lee aspects and cross loaded features. Any recently formed wind slabs should mainly be confined to the terrain above treeline, but in some areas wind slabs may have formed in the upper elevations of the below treeline, so evaluate the snow and terrain carefully Tuesday. Be cautious for shallow new snow to mask earlier formed wind slabs in exposed terrain.

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

The most recent warm and wet SW storm arrived on Valentines Day 2/14 and formed the uppermost strong rain crust in our snowpack in the Central-East and Southeast Cascades while only a thin freezing rain crust was observed 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.

A period of increasing westerly ridgetop winds Saturday afternoon was noted at the Mission Ridge and Dirty Face Peak weather stations and by guides in the Washington Pass area. Light snow showers over the past two days has deposited about 2-6 inches of low density snowfall along the east slopes of the Cascades from Sunday through Monday afternoon, with generally light winds and cold temperatures.

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, were shallow wind slabs formed late 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.