Avalanche Forecast

Archived

Feb 2nd, 2018–Feb 3rd, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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Dangerous avalanche conditions will exist throughout the area Saturday. Avoid steep open slopes at all elevations where you are likely to trigger an avalanche. Large natural Loose Wet avalanches were reported Friday indicating a dangerous and active cycle.

Detailed Forecast

Warm weather and precipitation will maintain dangerous avalanche conditions Saturday. Avalanche problems will be dependent on precipitation type.

Stay off of steep slopes with wet surface snow where you are likely to trigger Loose Wet avalanches. Natural Loose Wet avalanches were reported Friday. Many of them grew large and traveled well into runout areas. This is a clear indication that this avalanche problem is active and should be respected.

Isolated Wet Slab avalanches could occur during periods of higher intensity rain. Wet Slabs are extremely difficult to predict and assess. Avoid avalanche terrain if you see signs of slab activity occurring during the day Saturday.

Above treeline, moderate to strong winds will continue to build Wind Slabs. Use visual clues such as blowing snow, plumes, fresh cornices, and uneven snow surfaces to detect building Wind Slabs. Avoid steep slopes where snow is being deposited.

Less precipitation in some areas Saturday will limit the development of avalanche hazard.

Snowpack Discussion

Warm wet weather Friday created moist to wet surface snow conditions up to 6500 feet. A natural Loose Wet avalanche cycle occurred Friday with peak warming and precipitation.

Above treeline, below freezing temperatures, additional snow, and moderate winds formed new Wind Slabs on a variety of aspects. Poor visibility and stormy conditions has limited observations at higher elevations.

Cornices throughout the area have grown very large.

Observations

Stevens Pass

NWAC Avalanche Forecaster Josh Hirshberg traveled in the Stevens Pass areas Friday. Josh noted numerous natural Loose Wet avalanches on all aspects. These avalanches ranged from small to large, with some travelling 1000 vertical feet. Rain created 6” of wet surface snow by Friday afternoon.

Snoqualmie Pass

Alpental Ski Patrol Thursday reported very large cornices along ridges in the Alpental Valley.

South

An avalanche professional in the Crystal backcountry Thursday noted lingering wind slab instabilities near ridges. By late in the day light rain was already effecting the below treeline bands.

Problems

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.

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.