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Avalanche Forecast

Archived

Apr 5th, 2014–Apr 6th, 2014

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

Regions

Stevens Pass.

A continued mix of winter like and spring conditions should continue early Sunday with increasing wet snow conditions by Sunday afternoon. 

Detailed Forecast

Updated Sun AM to increase avalanche danger, especially storm slab near and above treeline and wet loose avalanche concerns lower in elevation.  3"-10" of new snow fell Saturday and Saturday night generally above 5000 feet along the west slopes.  Also, watch for and generally avoid weakened cornices along ridges. 

A front with increasing clouds and moisture will move across the region Saturday night, then east of the area Sunday. This is expected to cause increased winds and increasing rain and snow with slightly rising snow levels late Saturday and Saturday night.

This system should build some new shallow wind and storm slab at higher terrain and increase surface wet snow conditions below tree line.   

Watch for natural avalanches, pinwheels and surface wet snow deeper than a few inches on any solar slope Sunday.  Watch for evidence of wind transported snow in the higher terrain.

Remember to watch for cornices if you venture onto the ridges and avoid slopes below cornices. Cornice failures are often seen during the transition to spring weather. Cornices have grown large recently and may break back further from the edge than expected. 

Snowpack Discussion

An upper low moved southward off the coast early last week and largely missed the Northwest. But locally strong east winds were seen mainly near and above treeline and mainly in the South Cascades. NWAC observers Tom Curtis on Mt Adams Tuesday and Dallas Glass on Mt. Rainier on Wednesday reported redistributed snow and cross loaded slopes. Dallas reported 20-40 cm of wind slab in the 6400-7500 foot range with natural avalanches on a variety of aspects. Older wind slab will not be listed as a concern due to anticipated new wind slab development Saturday night.

A fair weather period with little avalanche activity was seen midweek.

A front crossed the Northwest on Thursday, causing moderately increasing winds, varied amounts of new snow and slightly lower snow levels. New snow amounts varied from 8-15 inches in the Mt Baker areas, including the Grouse Mtn area. The areas around Paradise on Mt Rainier received 8-10 inches with most other west slope Cascade areas 4 inches or less.

Following the front Thursday, the Mt Baker and Alpental patrol reported active results from ski and explosive control work. 

By Saturday, the storm layers had settled significantly with slope testing by ski and explosives in both the Baker and Alpental areas producing limited to no results.  Some shallow wet snow conditions were reported below tree line at Alpental by Saturday afternoon. 

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.

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.