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Avalanche Forecast

Archived

Mar 20th, 2015–Mar 21st, 2015

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

Regions

Stevens Pass.

A spring mix of avalanche problems will be possible Saturday with new storm and wind slab concerns near and above treeline, and loose wet possibilities on steeper solar aspects in the afternoon. There's a fair amount of uncertainty with the forecast Saturday, so be attuned to quickly changing snow conditions, especially if traveling above treeline.  

Detailed Forecast

A frontal system passing through Friday night should bring light to moderate rain and snow along with a cooling trend by Saturday morning.  Post frontal showers could locally be intense as the air mass destabilizes Saturday morning. Moderate SW winds will transport snow onto lee easterly aspects near and above treeline. 

Despite the cooling trend, there should be some shallow storm and wind slab near treeline by Saturday morning. New snow that does accumulate will be susceptible to potential sunbreaks later Saturday afternoon, so use extra caution on steeper solar slopes above treeline. Locally intense showers Saturday could contain graupel and quickly lead to sensitive storm slabs. 

Less recent snow and ample terrain anchors should greatly limit the avalanche danger below treeline. 

Remember the NWAC forecast applies to elevations up to the Cascade crest (~7000 to 8000 ft). Significant new snowfall from late this week likely poses a higher avalanche danger at these elevations in the Mt. Baker area.   

Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow to cause an avalanche danger.

Snowpack Discussion

During the storm cycle the weekend of March 14-15th, several inches of water fell with new snow above 6000-7000 ft in the south Cascades and above 4500 ft in the north Cascades. Natural or skier triggered slides that occurred Sunday or Monday were generally loose wet size D1-D2, and to a lesser extend storm slabs, and reported throughout the west slopes of the Cascades relative to last weekend's snowline.

A few inches of snow accumulated along the west slopes of the Cascades Tuesday above 5000 feet. Observations on Wednesday noted small loose wet avalanches involving the new storm snow near and above treeline. 

More significant new snowfall likely accumulated above 6000 feet in the Mt. Baker area Thursday and Friday, but there have been no recent observations in this terrain. 

The Chinook DOT crew on Monday found debris from an natural cycle of loose or storm slab avalanches from Sunday.

 

You are likely to encounter debris from last weekend if traveling above 6000 ft this weekend. Photo J. Stimberis.

The snowpack at low elevations remains meager to non-existent with the average snow-line around 4500 feet along the west slopes. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

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.

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.

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.