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Archived

Avalanche Forecast

Feb 15th, 2018–Feb 16th, 2018
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
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
1: Low
The avalanche danger rating below treeline will be low

Regions: Olympics.

You will still be able to trigger small isolated older wind slabs near ridgeline Friday. Identify and avoid slopes where the wind has deposited snow such as below fresh cornices and on wind drifts. Loose surface snow is covering an old firm crust. Be careful if you travel on steep icy slopes where it will be difficult to stop a fall. 

Detailed Forecast

Currently several inches of snow are anticipated to fall on Friday along with moderate ridgetop winds. The older snow should be more difficult to transport. However, if more fresh snow falls than anticipated, expect these moderate winds to form small wind slabs that are slightly more touchy than forecast, but still on specific lee slopes.

Small isolated wind slabs will linger into Friday on wind exposed areas near and above treeline. You are most likely to trigger these avalanches on steeper slopes below fresh cornices and on snow drifts. Identify and avoid areas of wind deposited snow.

In sheltered areas, weak sugary surface snow is present over a firm crust.  Use caution if traveling on steep icy slopes where stopping a fall may be very difficult.

Elsewhere in the Hurricane Ridge area generally safe avalanche conditions exist. Look for signs of unstable snow and monitor the weather throughout the day.

 

Snowpack Discussion

Several inches of weak old surface snow exists around the Huricane Ridge area. Near surface facets and surface hoar were observed on all aspects near treeline. In exposed terrain, SW winds transported snow forming small shallow isolated wind slabs on lee slopes.

Below the weak surface snow a strong firm crust exists. 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 sugary surface snow (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: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1