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Avalanche Forecast

Archived

Mar 31st, 2015–Apr 1st, 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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Don't be fooled on April 1st and watch for shallow yet sensitive slab avalanches involving new snow on lee easterly slopes near and above treeline as well as loose wet avalanches on solar slopes during sunbreaks and daytime warming Wednesday. Moderate danger mainly applies closer to the Cascade crest and lower avalanche danger is expected further east. 

Detailed Forecast

Additional light snow accumulations are expected near the Cascade crest Tuesday night through Wednesday with little to no accumulations further east. Moderate westerly transport winds are expected to ease Tuesday night. Showers may be locally intense Wednesday afternoon due to the unstable air mass over the region. 

Moderate danger means heightened avalanche conditions on specific slopes. Watch for shallow yet sensitive slab avalanches involving new snow on lee easterly slopes near and above treeline as well as small loose wet avalanches on solar slopes during sunbreaks and daytime warming Wednesday. Shallow slabs may fail on graupel layers from Tuesday. 

Cornices won't be listed as an avalanche problem but be aware of new cornice growth along ridgelines.

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

Snowpack Discussion

A warm front caused only light amounts of rain and snow east of the crest Wednesday to Thursday morning with gradual warming along the east slopes. NWAC Observer Tom Curtis was on Nason Ridge on Thursday and reported small to medium rollerballs and evidence of recent small to large loose wet avalanches.

A front crossed the Northwest Friday night causing strong west-southwest winds, some rain and snow and lowering snow levels, but new snow amounts were light east of the crest.

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

Snow levels fell quickly after a front moved through early Tuesday morning. Scattered showers near the Cascade crest through Tuesday afternoon deposited an inch or two near and above treeline. In many areas the old moist surface should be slowly re-freezing with the new snow generally bonding well, keeping avalanche concerns confined to new storm snow layers. 

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

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.