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Archived

Avalanche Forecast

Jan 10th, 2016–Jan 11th, 2016
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.

New small shallow storm and wind slab seems possible by the end of the day on Monday at Hurricane. Evaluate snow and terrain carefully on Monday. Adjust your plans if winds are stronger or new snowfall is heavier than expected.

Detailed Forecast

A front should weaken as it moves over the Northwest on Monday. Over the Olympics this should bring moderately increasing southwest alpine winds and mostly light occasional moderate rain or snow Monday morning changing to showers Monday afternoon with lowering snow levels.

Wet surface snow from Sunday should refreeze on Monday. 

New small areas of shallow storm slab seem possible mainly above treeline near Hurricane. The limited amounts of new snow and the cooling trend should limit the extent and depth of new storm slab by the end of the day.

New small areas of shallow wind slab also seem possible mainly on lee slopes at Hurricane by the end of the day. The limited amounts of new snow and the cooling trend should also limit the extent and depth of new wind slab.

 

Snowpack Discussion

Deep storm snow from late December should be settled and stabilized at Hurricane. About 6 inches of snowfall was seen at Hurricane last week.

NWAC pro-observer Matt Schonwald was at Hurricane on Friday and generally found a right side up stable snowpack. Older wind slab was limited to 15-30 cm pockets near ridges and tests indicated little propagation.

New surface hoar was seen primarily on sheltered north to east slopes which will need to be watched in case it is buried by future snowfall.

Avalanche Problems

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: Alpine.

Likelihood: Possible

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.

Likelihood: Possible

Expected Size: 1 - 1