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Avalanche Forecast

Archived

Mar 26th, 2015–Mar 27th, 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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Moist to wet surface snow should make loose wet slides remain possible Friday, especially before cooler and cloudier weather arrives late Friday. Also, watch for recently formed soft cornices along ridges.

Detailed Forecast

Increasing clouds with initially very mild temperatures early Friday should gradually turn to light rain and snow by afternoon with gradually lowering freezing levels. A frontal passage Friday night should cause some new snow, but only light amounts are expected. 

Strong melt freeze surface snow should gradually cool with some isolated and shallow wind or storm slabs developing by late Friday at higher elevations. 

Recent fresh cornices along ridgelines may still be soft and reactive, likely being weakened by sunshine and warming Thursday. These should remain susceptible to failure Friday. Make sure to give them a wide berth, and be aware of corniced slopes above you. 

Less recent snow and ample terrain anchors may limit the avalanche danger below treeline. Many areas at the lowest elevations 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 a foot and has likely been 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.

Only light amounts of rain and snow fell Wednesday along with a gradual warming trend along the east slopes. 

Sunshine and very warm temperatures Thursday has likely created significant surface snowmelt and should lead to a firm melt-freeze crust by Friday. 

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

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.