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Archived

Avalanche Forecast

Feb 4th, 2016–Feb 5th, 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
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

Wind slabs formed Wednesday, as well as expected continued wind transport Thursday, should maintain dangerous avalanche conditions, especially near and above treeline on a variety of aspects.

Detailed Forecast

Light showers are expected Thursday with moderate WSW ridgetop winds. Light expected precipitation amounts and gradual warming should allow for settlement, however, winds may still be strong enough to transport loose surface snow and continue to deposit wind slabs on lee aspects, more NE-E-SE facing. 

Watch for signs of cracking or firmer wind transported snow. 

New snow may have initially bonded poorly to a variety of snow surfaces Wednesday, including weak lower density snow on sheltered and shaded slopes, or a possible thin sun crust on southerly facing slopes. Travel cautiously and make route choice decisions conservatively Thursday. 

 

 

Snowpack Discussion

Heavy rain fell in the Olympics last Wednesday and Thursday (1/27-1/28) with over 2 inches of rain recorded    at the Hurricane Ridge NWAC station. 

The "20th of June" path released as a wet slab during the rain and warmth last Thursday. Photo: January 29th by Matt Schonwald.

A strong front last Friday brought 14 inches of new snow for the 2 days ending Saturday morning. This storm snow has accumulated on top of the most recent rain crust.

NWAC pro-observer, Matt Schonwald visited Hurricane on Friday, January 29th and found rapidly building wind slab and extensive loading on lee slopes in all 3 elevation bands. New cornices were sensitive to triggering but still relatively small. 

No new observations have been received since Friday. Cool weather with some light snow showers occurred over the Olympics Sunday and Monday while Tuesday was cool and partly sunny. The recent weather should have promoted stabilization of the most recent storm snow above the rain crust. 

A front is depositing new snow with strong winds Wednesday afternoon, 2/3. Likely building new storm and wind slabs on a variety of aspects, with wind slab expected, mainly on NW-N-NE facing slopes below ridges, near and above treeline.

 

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: Likely

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