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Avalanche Forecast

Archived

Jan 21st, 2018–Jan 22nd, 2018

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.

Significant snowfall has accumulated in the Olympic region over the past several days. While a break in the weather Monday will allow wind and storm slabs time to heal, they are expected to remain reactive. Avalanches may exhibit wider propagation and more significant snow entrainment than you expect. Continue to be cautious Monday if traveling in the backcountry.

Detailed Forecast

A break in the weather Monday will begin to allow wind and storm slab weaknesses time to heal.

Winds slabs formed over several stormy days will continue to be reactive Monday. Expect firm wind slabs which may trigger well above a backcountry traveler. Identify and avoid areas of wind deposited snow such as snow drifts and slopes below cornices. Due to the strong winds accompanying heavier precipitation on Sunday, expect wind deposited snow will be found well below ridgeline.  

Storm snow weaknesses formed throughout the last several days will become increasingly difficult to trigger. However, once triggered, an avalanche has significant recent snow to work with and may be large, entraining significant amounts of snow. Avoid large open slopes where avalanche may propagate more widely to become larger than you might anticipate.

Significant, settling new snow warrants continued caution.  

Tree wells and snow immersion are a growing concern in the Olympic area. Maintain communication with your partners as you travel.

Snowpack Discussion

Storm snow continues to accumulate in the Olympic area. Roughly 3 feet of snow rest above the most recent crust layer on sheltered slopes. Fluctuations in temperature and snowfall intensity during Sunday's storm created several storm snow weaknesses.

Strong southerly winds throughout the day on Sunday formed wind slabs on lee slopes near and above treeline.

Most recent observations show the recent storm snow bonding well to the 1/16 crust layer. Observations from this region are limited. A high degree of uncertainty exists in this area.

Observations

NWAC observer Matt Schonwald traveled in the Hurricane Ridge terrain Thursday, Jan 18. In general, Matt found right side up new snow bonding well to the underlying old snow surface. In exposed terrain, winds on Thursday were actively transporting new snow and building sensitive slab layers.

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.