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Avalanche Forecast

Archived

Mar 22nd, 2015–Mar 23rd, 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

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There may be some shallow storm and wind slab above treeline Monday. Any new snow that does fall will be susceptible to sun breaks later Monday afternoon, so use extra caution on steeper solar slopes near and above treeline. 

Detailed Forecast

 

Light to moderate showers are expected as an upper trough passes Monday. Freezing levels should lower Monday, but be tapered by daytime warming.  Increasing SW ridge top winds may build shallow new wind slabs on some lee slopes, mainly below ridges on N-NE facing terrain near and above treeline. 

Any new snow that does fall will be susceptible to sun breaks later Monday afternoon, so use extra caution on steeper solar slopes above treeline. 

Less recent snow and ample terrain anchors should greatly limit the avalanche danger below treeline, especially in the south and central Cascades. 

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

The 15-18 inches of snow that fell a week ago has now been absorbed into the upper snowpack and settled or melted by at least 10 inches. 

The observations from last week regarding the last week's storm snow are now mostly inapplicable as daily warming has made the upper snowpack now mostly homogeneous.

The latest frontal systems Friday night and again Sunday only deposited very light amounts of new snow to the east slope areas, so there is not a great deal of new snow instabilities to deal with.

Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and lower elevation slopes for the central and southeast Cascades.

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.

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.