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Avalanche Forecast

Archived

Apr 6th, 2015–Apr 7th, 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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Due to a fair amount of uncertainty with the weather forecast, a moderate hazard rating will be forecast above treeline, however watch for local areas that have received greater recent snowfall where a locally greater danger may exist.

Detailed Forecast

A slowly changing weather pattern will maintain cool weather, light winds and isolated showers again Tuesday.  Only light amounts of new snow are expected Monday night through Tuesday.  Due to the showery nature of the expected precipitation, a fair amount of uncertainty is expected with the subsequent hazard forecast. A moderate hazard rating will be maintained above treeline for any new storm snow problems. However, in areas that receive little or no new snowfall through Tuesday afternoon... expect a lower local avalanche danger than the regional forecast. 

Shallow storm slabs may develop Tuesday in areas that receive greater shower activity. It's April, so be aware of the increased solar input reaching more aspects and affecting the snow surface quickly. Loose wet avalanches involving shallow amounts of recent storm snow will be also be possible Tuesday, especially during sunbreaks in the afternoon. 

Small loose dry avalanches are also possible for non-solar aspects at higher elevations. Loose dry avalanches won't be listed as a top avalanche problem, but be aware of fast moving sluffs knocking you off your feet and into unintended terrain traps on steeper slopes. 

Due to the continued cool weather, cornices won't be listed as an avalanche problem either, however use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.

Snowpack Discussion

The recent active weather since about mid March onward has brought periodic light snowfalls east of the crest and allowed general snowpack consolidation and stabilization. 

A front moved across the Northwest Tuesday, followed by showers and rapid cooling, but caused little snow east of the crest except locally downwind of a convergence zone centered on Snoqualmie Pass.

A TAY report from Mt. Stuart Thursday reported 6-12" of unconsolidated snow even on solar aspects above treeline, likely a benefactor of Tuesday night's convergence zone. NWAC observer Jeremy Allyn was in the Washington Pass area over the Easter weekend and found a few inches of recent snow on a thick crust that needed additional loading to become problematic. Greater recent storm snow was being preserved west of Rainy Pass where about 10 inches of great unconsolidated powder was being maintained on shaded terrain at higher elevations, providing a bit welcomed powder skiing!

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

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.