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Avalanche Forecast

Archived

Dec 13th, 2015–Dec 14th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

The strong storm Saturday, and subsequent additional snowfall Sunday should maintain widespread wind and storm slab layers on lee slopes near ridges Monday. Travel conservatively by staying off or below steeper slopes and avoid wind loaded terrain, especially but not limited to northwest through southeast facing terrain.

Detailed Forecast

A few isolated snow showers may linger Monday, while winds should be light and temperatures remain cool. 

This should allow for a slowly improving avalanche danger as recent storm and wind slabs begin settling and stabilizing.

However, storm and wind slab conditions should remain sensitive or still likely to trigger in specific areas and more widespread areas above treeline from very strong winds Saturday. North to east facing lee slopes will continue to be loaded and slower to stabilize.  

Dangerous avalanche conditions are expected above tree line requiring conservative decision-making and cautious routefinding.

Be cautious with any steeper open terrain suspected of recent wind loading, leaving those more exposed features a wide margin of safety.

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 44 inches Sunday morning with 28 inches new snow received since Tuesday.  

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.  Another strong storm Saturday, with very strong winds and snow, followed by additional snow Sunday, but with lighter winds has changed the upper snowpack significantly since Friday. An additional 15-20 inches have accumulated since Friday. A report by Park Ranger at Hurricane Ridge Sunday midday reported a soft slab release below the Sunrise Ridge area near Hurricane. The slide was likely triggered, however that was not confirmed.  The avalanche crown was estimated at 2-3 ft and released about 150 wide and ran about 100 feet vertical, certainly big enough to get into serious trouble. Terrain anchors are rapidly being buried by recent snowfalls but may still add significant anchoring in many areas below 4-4500 feet.  

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.