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Avalanche Forecast

Archived

Mar 18th, 2015–Mar 19th, 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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Watch for previous wind slab and loose wet avalanche conditions east of the crest on Thursday.

Detailed Forecast

A southwest-northeast oriented front will move slowly to the International border area on Thursday with a series of waves beginning to move along the front. But the east slopes should remain generally dry through the daylight hours on Thursday.

Watch for previous wind slab on previous lee slopes. Loose wet avalanches should also remain possible especially on solar slopes. The avalanche danger will be regionally higher in the northeast Cascades where there has been more recent snowfall.

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

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.   

Over the 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 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. Storm snow amounts in that region averaged about 16 inches near and above treeline by late Sunday.

A weak front may have caused minor rain or snow at higher elevations on Tuesday.

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.

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.