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Avalanche Forecast

Archived

Apr 2nd, 2015–Apr 3rd, 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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Changing weather will require careful snow and terrain evaluation west of the crest by Thursday afternoon.

Detailed Forecast

A moderate front and short wave trough will cross the the Northwest on Friday afternoon and evening. Rain or snow should begin over the Cascades Friday afternoon.

Increasing winds and increasing snow mainly above and near treeline west of the crest should begin to build new wind and storm slab Thursday afternoon. These new layers should still be fairly shallow by the end of the afternoon. The danger will be greater if the snowfall begins sooner or is heavier than expected by the end of the afternoon.

New wind and storm slab should continue to build Friday evening especially if convergence is significant near Stevens Pass.

Even though Friday should overall be cool and cloudy it is April and the sun is getting much stronger. So possible loose wet avalanches involving recent storm snow will remain in the forecast as well and emphasized for solar slopes.

Snowpack Discussion

Active weather and periods of snowfall have been seen since about mid March with some avalanche cycles and also periods of consolidation and stabilizing. The largest avalanche cycle was at Mt Rainier March 25th.

The latest front moved across the Northwest Tuesday followed by showers and rapid cooling Tuesday night and Wednesday. Storm snow from this system ranged from about 3-10 inches along the west slopes except at Snoqualmie with 15-20 inches in strong convergence Tuesday night.

A bit surprising has been the reports from ski patrols at Alpental and Crystal Mountain Wednesday that the new snow quickly settled with little to no avalanche activity. There was evidence at Alpental that a natural cycle occurred before daylight Wednesday likely during some heavy loading in the early morning hours.  A testament to how quickly new snow is able to settle and stabilize as we move into April. By Wednesday afternoon, the snow had settled 6 inches at the Snoqualmie Pass level from the early morning depths.

A cool to mild day on Thursday is mainly causing of consolidation and stabilizing. The Alpental patrol had no avalanches to report on the upper mountain on Thursday with recent surface snow getting heavy on solar slopes and staying cool and light on north slopes.

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 the lowest elevations 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.