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Avalanche Forecast

Archived

Feb 4th, 2016–Feb 5th, 2016

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

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.

 

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.