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Avalanche Forecast

Archived

Mar 19th, 2015–Mar 20th, 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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Loose wet avalanches and shallow new and older wind slabs are possible near and above treeline Friday.  Loose wet avalanches will mostly likely involve the new snowfall received Thursday and Thursday night above 6000 ft.    

Detailed Forecast

An approaching frontal system should cause a general increase in clouds and winds throughout the day, but significant precipitation is unlikely until Friday night for the east slopes. 

Loose wet avalanches and shallow wind slabs are possible near and above treeline Friday, and will mostly likely involve the new snowfall received Thursday and Thursday night above 6000 ft.    

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 latest installment of warm and dry weather lasted from early to mid-March and led to more snowpack consolidation and a scarcity of avalanche activity. Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and low elevation slopes for the central and southeast Cascades.   

Last weekend, another warm wet SW flow brought a one-two punch to the Pacific Northwest. Saturday's event brought up to 1.0 inches of water with a snow level around 6500 feet through Saturday afternoon, with much lower totals in the Blewett-Mission Ridge area. 

Another inch or more of water fell more evenly along the east slopes Sunday and Sunday night, with the snow level around 4500-5000 feet in the north and about 6000 feet in the south. Around 15-18 inches of snow fell at the NWAC Washington Pass station and the Hart's Pass Snotel by Monday morning.

NWAC observer Jeff Ward was in the Hart's Pass area over the weekend and reported growing storm and wind slab concerns by late Saturday afternoon. He saw easily triggered small storm slab and dry loose near the 6000 feet elevation.   

NWAC observer Tom Curtis was on Nason Ridge near Stevens Pass on Wednesday and found ongoing possible loose wet avalanche conditions on solar slopes and lingering shallow wind slab on northwest to northeast slopes.

Light snowfall fell in the north Cascades above 6000 ft Thursday with moderate southwest transport winds. 

Problems

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.

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.