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Avalanche Forecast

Archived

Dec 11th, 2015–Dec 12th, 2015

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

Regions

Olympics.

Expect deteriorating snow stability as the day progresses and the storm really takes hold. Travel conservatively by staying off steeper slopes and avoiding wind loaded northerly terrain, especially later in the day,

Detailed Forecast

Snow will begin by mid-morning and increase in intensity throughout the day. In addition, there should be a gradual warming trend as snow levels peak between around 4500 feet in the late afternoon. Combined with increasing southerly transport winds in the afternoon, there will be an increasing avalanche risk through the daylight hours. 

Storm slabs should become more sensitive and likely to trigger in the afternoon. Northerly lee slopes will continue to be loaded throughout the day as well.  

Expect deteriorating snow stability as the day progresses and the storm really takes hold. Travel conservatively by staying off steeper slopes and avoiding wind loaded northerly terrain, especially later in the day,

Be aware of early season hazards below treeline. The heavy rains from last week have left many creeks open at lower elevations. 

Snowpack Discussion

After a wet week that culminated with heavy rain Monday and Tuesday knocking the Waterhole snowdepth (5000 ft) down to around 18 inches, we have returned to colder snow levels with new snow. The NPS ranger at Hurricane Ridge reported a snowdepth of 34 inches Friday morning with 14 new inches received since Tuesday. 

Avalanche and Snowpack Observations

NWAC pro-observer Matt Schonwald was at Hurricane Ridge Friday, taking the first set of snowpack observations in the Olympic zone for NWAC this season.  Matt found a snowdepth averaging around 1 meter (over 3 ft) with slightly more snow in less wind affected areas. The most recent snow has bonded well to the old surface and there were no significant storm snow instabilities. However, there were signs of significant wind loading onto open lee NE slopes, mainly applicable to the near and above treeline elevation bands.  Below treeline should still contain ample terrain anchors, but above 4000'-4500' there is enough snow to allow avalanches in specific areas. 

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.