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Avalanche Forecast

Archived

Apr 9th, 2015–Apr 10th, 2015

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

Regions

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It's the calm before the weekend storm: Friday's avalanche concerns should be limited to small and localized pockets of wind slab on lee aspects and small wet loose on solar aspects with both problems found mainly above treeline.  

Detailed Forecast

An approaching Pacific frontal system should increase cloud cover along the west slopes Friday afternoon and bring a significant uptick in SW winds. Significant new snow and rain should hold off until Friday evening across the west slopes.    

The avalanche danger Friday should be limited to small and localized pockets of wind slab on lee aspects and small wet loose on solar aspects with both problems found mainly above treeline.  

It's April, so be aware of the increased sun effects reaching more aspects and affecting the snow surface fairly quickly. Loose wet avalanches involving shallow amounts of recent storm snow will be possible, especially in any direct sun on solar slopes earlier in the day.  

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

Snowpack Discussion

A broad upper trough moved over the Northwest last weekend through early this week causing periods of light snow west of the crest at low snow levels. On Wednesday and Thursday, clear skies transitioned to scattered afternoon showers with light and spotty new accumulations. April freezing levels have been very low compared to most of the winter, averaging about 4-5000 feet thus far.

Backcountry reports from across the Cascades near and above treeline indicate cool, preserved snow on non-solar aspects with limited wind effects (see exception below), gradual settlement and generally good bonds to the previous crust.  On solar aspects, sun breaks have caused only small loose wet avalanches and crusts. Some large cornices continue to be reported along ridges especially in the north Cascades. 

A TAY report from Wednesday in Glacier Basin MRNP and NWAC observer Dallas Glass on the SW side of Mt. Rainier Thursday noted small and local wind slab lingering above treeline.  

Snowpack problems west of the crest should remain in the upper or surface layers. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this season. Many areas at lower elevations do not have enough snow to cause an avalanche danger.

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.

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.