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Avalanche Forecast

Archived

Mar 30th, 2015–Mar 31st, 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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Moderate danger mainly applies closer to the Cascade crest and lower avalanche danger is expected further away from the Cascade crest Tuesday. Increasingly sensitive avalanche conditions involving shallow amounts of new snow are possible on lee slopes near and above treeline as well as loose wet avalanche concerns during sunbreaks and daytime warming Tuesday afternoon. 

Detailed Forecast

A frontal system passing through late Monday night should be followed by orographic showers and a cooling trend Tuesday. Showers may be locally intense near the Cascade crest Tuesday afternoon with more moderate snowfall accumulations possible for the east slopes downwind of a Puget Sound convergence zone between Stevens and Snoqualmie Passes. 

Moderate danger mainly applies closer to the Cascade crest and lower avalanche danger is expected further away from the Cascade crest Tuesday. Increasingly sensitive avalanche conditions involving shallow amounts of new snow are possible on lee slopes near and above treeline as well as loose wet avalanche concerns during sunbreaks and daytime warming Tuesday afternoon.    

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

The 1-2 feet of snow that fell in mid-March east of the crest, mainly in the northeast Cascades, has settled into the upper snowpack. 

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 and short wave crossed the Northwest Friday night causing strong west-southwest winds, some rain and snow and lowering snow levels. But rain and snow amounts were light east of the crest.

During the mild and fair weather Monday, avalanche professionals working in the Washington Pass area caused 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. One size-able wet loose avalanche was observed off of Kanagroo Ridge as well Monday. 

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.