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Avalanche Forecast

Archived

Apr 3rd, 2015–Apr 4th, 2015

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

Regions

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New snow should require careful snow and terrain evaluation at higher elevations east of the crest Saturday.

Detailed Forecast

Weak flow and mostly light showers should move out of a low or form over the Northwest in a cool slightly unstable air mass Saturday afternoon. These showers may be more likely during the afternoon hours and at higher elevations east of the crest.

Watch for possible new small wind and storm slab from Friday. These layers would be deeper if you find an area that had more snowfall.

It is April and the sun is getting much stronger. So possible small loose wet avalanches will remain in the forecast as well. Solar slopes in any area with significant new snow from Friday will be very susceptible on Saturday.

Cornices won't be listed as an avalanche problem but use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.

Snowpack Discussion

Active weather has been seen since about mid March but there has been little snowfall overall east of the crest. So consolidation and stabilizing has been mainly seen east of the crest the past couple weeks.

During the fair and mild weather Monday, DOT avalanche professionals working in the Washington Pass area triggered significant slides Monday using explosives. Wet slab avalanches entrained moist snow in the Liberty Bell paths and buried the closed highway with about 8 feet of debris. But little natural avalanche activity was observed in the area. 

A front moved across the Northwest Tuesday followed by showers and rapid cooling. But this caused little snow east of the crest.

NWAC observer Jeremy Allyn was at Washington Pass on Friday morning and only found about an inch of recent snow on a thick crust. He commented this would be a good set up for wind and storm slab if there is significant new snowfall.

Another front and short wave trough are crossing the Northwest Friday afternoon. This should be accompanied by moderate southwest winds and mostly light rain or snow east of the crest. Snow showers at higher elevations should decrease pretty rapidly Friday evening. 

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. Many areas at lower elevations and further away from the Cascade crest do not have enough snow to cause an avalanche danger.

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.

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.

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.