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Avalanche Forecast

Archived

Dec 10th, 2015–Dec 11th, 2015

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

Storm concerns should decrease through the day Friday, but watch for sensitive new storm and wind slab, especially on lee N through SE slopes near and above treeline. Careful route-finding and snow evaluation will be essential. 

Detailed Forecast

Showers should diminish overnight through Friday morning.  A low pressure system diving south should largely miss the Olympics Friday with partly sunny skies expected in the afternoon.

Watch for sensitive new storm and wind slab, especially on lee N through SE slopes near and above treeline. Although we can make an educated forecast about the snowpack stability in the Olympics, carefully evaluate the snow and terrain for yourself.   

 

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 snow levels and a snowdepth of around two feet as of this morning. Several more inches have likely fallen through the day with predominately SW winds at ridgetop. 

Avalanche and Snowpack Observations

Given the warm, wet weather over the Olympics earlier in the week, it is likely that the upper snowpack has consolidated and drained. We will likely have built new, shallow and potentially unstable storm snow layers within the last 24 hours, especially on leeward slopes near and above treeline. Below treeline should still contain ample terrain anchors, but above 4000'-4500' there is likely enough snow to allow small avalanches in specific areas. 

While we have not had a specific snowpack observation from Hurricane Ridge thus far this season, new NWAC observer Matt Schonwald will be taking observations from Hurricane Ridge beginning this weekend! 

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.