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Archived

Avalanche Forecast

Feb 6th, 2017–Feb 7th, 2017
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
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

Regions: Olympics.

New snow instabilities within the deep recent snowfall will continue to settle out, but continue to make conservative terrain choices by choosing lower angled terrain and avoiding wind loaded slopes. Recently formed wind slabs may be found on a variety of aspects Tuesday. 

Detailed Forecast

Showers should end Tuesday morning. Cold temperatures and light winds are expected Tuesday. This should allow for slow settlement and stabilization of recent wind and storm slabs formed during the storm cycle since Friday.

Storm slabs may still be sensitive on Tuesday, but likely confined to the most recent storm snow over the past day. While deeper storm slab instabilities should be stabilizing, it may still be possible to trigger a large storm slab avalanche in isolated areas. 

Be aware that small loose dry avalanches triggered on steep slopes can entrain deeper snow layers.   

Instabilities within the deep new snow may need more time to settle out so make conservative terrain choices by choosing lower angled terrain and avoiding any wind loaded slopes, mainly near and above treeline. 

Snowpack Discussion

Weather and Snowpack

A strong storm cycle began Friday, continuing into Monday afternoon. As of Monday afternoon the three day storm totals have been about 2-3 inches of water equivalent with about 2.5 feet of snow accumulating in the Hurricane Ridge area. A cooling trend began Friday afternoon with a gradual decrease in overall snowfall intensities from Sunday morning. Winds through the storm cycle have been mostly light to moderate at times.

Melt-freeze crusts formed a week ago during high freezing levels and light rain. 

Recent Observations

NWAC pro-observer, Matt Schonwald was at Hurricane on Friday (before most of storm snow arrived) and found scoured slopes or shallow new snow on E slopes and shallow building wind slab on SW slopes. He found no significant signs of instability, ski tracks still visible from last week and lots of surface roughness to fill in on lee slopes.

No observations were received Saturday through Monday. 

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: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1

Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1