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Avalanche Forecast

Archived

Dec 12th, 2015–Dec 13th, 2015

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

Regions

Olympics.

The strong storm Saturday should have created widespread new storm layers and new unstable wind slab on lee slopes near ridges by Sunday with further snowfall and winds expected during the day Sunday. Travel conservatively by staying off or below steeper slopes and avoid wind loaded north and east facing terrain.

Detailed Forecast

Snow showers will continue Sunday with moderate ridge top winds. Temperatures should remain cool.

Recent storm and wind slabs may continue to build and storm layers from Saturday and Saturday night will not have settled or stabilized by Sunday. 

Storm slabs should remain sensitive and likely to trigger. North to east facing lee slopes will continue to be loaded throughout the day as well.  

Dangerous avalanche conditions are expected near and above treeline requiring conservative decision-making and cautious routefinding.

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, melting the Waterhole snowdepth (5000 ft) down to around 18 inches, winter has returned to lower snow levels and new snow. The NPS ranger at Hurricane Ridge reported a snowdepth of 34 inches Friday morning with 14 new inches received since Tuesday. Stormy conditions early Saturday curtailed an observation. 

Avalanche and Snowpack Observations

NWAC pro-observer, Matt Schonwald was at Hurricane Ridge Friday, collecting the first snowpack observations in the Olympic zone for NWAC this season, welcome Matt! The snowdepth averaged 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 in 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.  No observations were received Saturday as a result of stormy conditions. 

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.