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Avalanche Forecast

Archived

Mar 24th, 2015–Mar 25th, 2015

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

Regions

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A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. This should cause a big increase in the avalanche danger on Wednesday including east of the crest.

Detailed Forecast

A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. Rain or snow should be heaviest in the Olympics and central to south Cascades Wednesday morning and shift to the north Cascades Wednesday afternoon and evening. Snow levels and avalanche danger levels will be a moving targets but the sure thing is they will be going up pretty rapidly on Wednesday.

East of the crest the warming trend and initial snow will help build new upside down new storm slab where there is at least a few hours of snowfall of an inch or more an hour. This is likely above treeline throughout the east slopes through the morning and then mainly in the north Wednesday afternoon and evening.

The warming trend and initial snow will also help build new wind slab on lee slopes. This is also likely above treeline throughout the east slopes through the morning and then mainly in the north Wednesday afternoon and evening.

A change to rain should generally be seen in the south during the morning and in the north in the afternoon and evening. This is likely to begin to cause a cycle of loose wet avalanches on many slopes in most elevation bands.

Less recent snow and ample terrain anchors should limit the avalanche danger below treeline. Many areas below treeline do not have enough snow to cause an avalanche danger.

Snowpack Discussion

The 15-18 inches of snow that fell about March 14th-15th mainly in the northeast Cascades has settled or melted by at least 10 inches and probably been mostly absorbed into the upper snowpack.

The storm last weekend only deposited light amounts of new snow to most of the east slopes.

The DOT crew working at Washington Pass on Monday and Tuesday reports mostly stable overall snow conditions with 4-6 inches of recent snow above the pass and about 2 inches at pass level. One natural loose dry avalanche was seen at about 6500 feet on Silver Star Peak on Tuesday.

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

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.