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Avalanche Forecast

Archived

Feb 27th, 2015–Feb 28th, 2015

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

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Winds slabs will be the primarily concern Saturday and should generally be found on non-traditional westerly aspects with significant wind loading. Careful route finding and attention to local loading patterns will be necessary to have a safe and enjoyable day in avalanche terrain.

Detailed Forecast

Moderate east winds will become northeasterly Friday night and continue significant loading of westerly aspects through mid-day Saturday. 

Winds slabs will be the primarily concern Saturday, so pay attention to the local loading pattern in your area, but generally expect non-traditional westerly aspects to have significant wind loading. Wind slabs may form further downslope of areas of stronger winds, a fact that may not be apparent until you've already committed to a slope.  

Lesser avalanche problems that are still possible are storm slabs where storm instabilities persist in wind sheltered terrain and loose wet avalanches on steeper solar slopes. The sun is strong enough at the end of February to activate loose wet avalanches even on cooler days. 

Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow (new or existing) to pose an avalanche hazard. 

Snowpack Discussion

Since the warm and wet start to February, fair weather through mid-February has led to generally thick surface crusts, as well as further deterioration of the snow cover below treeline. 

After some light snow accumulations midweek along the west slopes midweek, 6-10 inches of new snow accumulated Thursday night and Friday above 4000 ft from Snoqualmie Pass and south, including Crystal Mt and Mt. Rainier. Generally an inch or less was received further north.  

Professional NWAC observer Jermey Allyn was at Paradise on Friday and found 25 cm (10 in.)  of new snow bonding well to previous snowfall received midweek and layering with a favorable density profile. By mid-day Friday, east winds were beginning significant snow transport near treeline and fresh wind slabs were developing on westerly aspects.  

The mid and lower snowpack west of the crest snow consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

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.

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.