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Avalanche Forecast

Archived

Jan 3rd, 2015–Jan 4th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Olympics.

The avalanche danger will increase sharply Sunday with human triggered slides becoming likely. Choose a conservative travel plan and make sure your plan allows for a safe exit if conditions deteriorate quicker than expected. 

Detailed Forecast

Light snowfall Saturday night and Sunday morning will increase in intensity Sunday afternoon along with increasing winds. A warming trend should lead to inverted storm snow by mid-day Sunday. Snow should change to rain at below and near treeline by Sunday afternoon. 

All of this will lead to quickly increasing avalanche danger Sunday. Expect human triggered avalanches to be likely as the day wears on. 

Natural loose wet avalanches will become very likely on steeper slopes with the change to rain. 

Storm slab avalanches releasing within the storm snow may step down to a variety of surfaces including recently formed crusts or the aforementioned graupel layer. Storm slabs will be more likely to trigger on wind loaded lee aspects. 

More significant warming and precipitation is expected Sunday night and a natural avalanche cycle is expected.  

Snowpack Discussion

A storm system hit the Northwest last weekend with strong west to northwest winds. The NWAC site at Hurricane picked up about 12 inches of storm snow with a good cooling trend. Strong northeast winds hit at the tail end of the storm Monday and Tuesday. This transported snow and formed some local wind slab on exposed slopes and near ridges but in most areas this layer bonded well and lacked underlying weak layers.

An upper ridge over the coastal waters tilted inland Wednesday and Thursday producing sunny weather and warm temperatures at higher elevations. NWAC observer Tyler Reid was at Hurricane Ridge on Wednesday and reported widespread small wet loose avalanches.

On Saturday, NWAC pro-observer Katy Reid confirmed a 3 cm graupel layer at 10 cm below the surface on E-NE aspects near and below treeline. This layer could become reactive during the upcoming storm. One of our biggest concerns heading into the upcoming storm will be the new storm snow's ability to bond to a variety of snow surfaces; near surface facets, wind board, melt-freeze crusts, etc.  

Graupel layer at Hurricane on Wednesday by Tyler Reid.

 

Problems

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.