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Archived

Avalanche Forecast

Feb 7th, 2016–Feb 8th, 2016
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

A warm and sunny day with freezing levels pushing above 12,000 feet Monday will point the avalanche danger toward loose wet avalanches. Steeper solar slopes should be the most likely places for natural or skier triggered loose wet avalanches. Solar slopes involve more than just due south aspects as we head further into February.  

Detailed Forecast

A warm and sunny day with lighter  winds should be seen on Monday. As freezing levels push above 12,000 feet, the avalanche danger will focus on loose wet avalanches. Steeper solar slopes should be the most likely places for natural or skier triggered loose wet avalanches. Solar slopes involve more than just due south aspects as we head further into February.  

Be aware of loose wet avalanche potential above terrain traps (like above cliffs or near gullies), where even small wet avalanches can become powerful and have unintended consequences.  

Lingering wind slab on lee slopes near and above treeline should be stubborn to trigger, but still possible in isolated locations on Monday. 

Snowpack Discussion

Cool, benign weather early last week formed a sun crust on many solar slopes and allowed surface hoar development on non-solar slopes.

A cold front and then a warm front crossed the Northwest on Wednesday and Thursday. The Hurricane ranger reported about 8 inches of snowfall for the 2 days ending Friday morning. No snowpack observations were received Friday due to the closed road. 

An additional 7 inches of snow fell with a cooling trend during Friday night's fast, yet powerful front. Lee slopes were likely loaded by strong S-SW winds with this system.

On Saturday, an observation on the NWAC page submitted by a professional guide identified a sensitive buried surface hoar layer on a north aspect near Hurricane Ridge.  Shooting cracks were observed, but no avalanche activity was observed on this layer.  

Also on Saturday, a NPS ranger reported a snowboarder triggered a wind slab avalanche on a NE aspect just outside of the ski area. The snowboarder was not caught, but the soft wind slab avalanche had a 1-2 ft crown. 

Warm temperatures, cloudy skies, and periodic light rain occurred on Sunday. 

Avalanche Problems

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.

Aspects: South East, South, South West, West.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 1

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: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1