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Archived

Avalanche Forecast

Feb 16th, 2018–Feb 17th, 2018
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
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
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.

Dangerous avalanche conditions exist. Avoid slopes over 30 degrees where the wind has deposited snow and fresh wind drifts.

Detailed Forecast

You can trigger large Wind Slab avalanches on steep slopes where you find at least 1 foot of freshly drifted snow. Watch for cracking in the snow, firm supportive fresh snow, and obvious blowing snow as indicators of Wind Slabs. You can stay safe by staying off of the obviously pillowed and drifted features.

You can trigger small Loose Dry avalanches where you find more than 6 inches of snow sitting on weak old snow or slick crusts on sheltered slopes. Significant snowfall and strong wind will maintain elevated avalanche conditions through the weekend. 

 

Snowpack Discussion

New snow is falling on slick old surfaces in the Hurricane Ridge area. Near surface facets and surface hoar were observed on all aspects near treeline. In exposed terrain, winds have scoured down to an old crust and formed drifts on lee slopes.

Below the weak surface snow there are no layers of concern. Warm wet weather from the first week of February has created a relatively uniform and consolidated snowpack. There are no significant layers of concern below the most recent crust.

Observations

NWAC professional observer Matt Schonwald and NPS rangers were on Mt Angeles Thursday. They observed 4 inches of weak sugar-like snow on the surface (near surface facets) on all aspects and elevations traveled. They were able to trigger a small isolated wind slab on an E aspect near treeline. No natural avalanches were observed.  

Avalanche Problems

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: All elevations.

Likelihood: Likely

Expected Size: 1 - 1