Avalanche Forecast

Issued: Feb 2nd, 2018 10:00AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Loose Wet and Wind Slabs.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

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.

Summary

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

An icon showing Loose Wet

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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.

 

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Elevations: Treeline, Below Treeline.

Likelihood

Likely

Expected Size

1 - 1

Wind Slabs

An icon showing Wind Slabs

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.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 1

Valid until: Feb 3rd, 2018 10:00AM