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Avalanche Forecast

Archived

Feb 13th, 2016–Feb 14th, 2016

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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

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The continued warming trend Sunday, strong winds and additional rain or snow will increase the likelihood of natural or triggered avalanches. Dangerous avalanche conditions are expected Sunday. 

Detailed Forecast

Increasing moderate to heavy rain and snow is expected with a warming trend Saturday night through Sunday. With the snow level expected to rise to near 6000 feet by early Sunday, a significant increase in avalanche danger is expected overnight with natural avalanches becoming likely. If a natural avalanche cycle occurs overnight, this should locally lower the danger during the day Sunday, at least in those areas that experienced avalanches. The main question is about the rate and timing of warming. If the warming is not as great as expected or delayed, a very heightened avalanche danger should persist into Sunday.

On slopes that have not released due to warming and additional load, natural or triggered avalanches should be increasingly likely Sunday.  

Strong W-SW winds will transport new snow onto lee slopes near and above treeline where wind-driven snow may build unstable wind slab on lee aspects. 

Wet loose avalanches will be a concern on steeper slopes at lower elevations.

Avoid cornices along ridges and slopes below cornices since cornices may still be weaker due to the warm weather.

Snowpack Discussion

Weather and Snowpack

The warmest weather of the winter occurred this past Sunday through Wednesday with extended temperatures climbing into the 50's in most areas, with some excursions into the 60's!  A warm front brought periods of rain to the west slopes Thursday night through mid-day Friday, with snow levels falling to 5000 ft after the frontal passage Friday afternoon. Further cool showers Saturday has combined to deposit storm snow amounts ranging from about 6-16 inches as of Saturday evening. 

The gradual cooling Friday changed rain to snow and caused a strong bond of new snow to the refreezing old wet snow surface as reported in the Mt Baker and Alpental areas Saturday. The upper snowpack should be well bonded to the 1/28 rain crust in all areas along the west slopes. 

Recent Observations

Reports from the Mt Baker pro patrol Saturday indicated the 14 inches of storm snow as of Saturday morning was happy to stay in place after the control from explosives and ski cutting attempts, as a result of the strong bonding to the underlying crust. 

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.

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.