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Avalanche Forecast

Archived

Mar 31st, 2015–Apr 1st, 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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Don't be fooled on April 1st and watch for shallow yet sensitive slab avalanches involving new snow on lee easterly slopes near and above treeline as well as loose wet avalanches on solar slopes during sunbreaks and daytime warming Wednesday.

Detailed Forecast

Additional light snow accumulations are expected Tuesday night through Wednesday along the west slopes, except in the Snoqualmie/Stevens area where accumulations near and above treeline may be closer to a foot. Moderate westerly transport winds are expected to ease Tuesday night. Showers may be locally intense Wednesday afternoon due to the unstable air mass over the region. 

Moderate danger means heightened avalanche conditions on specific slopes. Watch for shallow yet sensitive slab avalanches involving new snow on lee easterly slopes near and above treeline as well as small loose wet avalanches on solar slopes during sunbreaks and daytime warming Wednesday. Shallow slabs may fail on graupel layers from Tuesday. Higher avalanche danger is expected above treeline in the Stevens to Snoqualmie zones where more snowfall is forecast.       

Cornices won't be listed as an avalanche problem but be aware of new cornice growth along ridgelines.

Snowpack problems west of the crest for the time being should be 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.

Snowpack Discussion

Winter-like conditions last week were followed by reports of natural and skier triggered loose avalanches on Tuesday, Mar 24th along the west slopes. This was followed by a warm front and heavy rain last Wednesday through Thursday morning. This caused an avalanche cycle west of the crest with many large natural avalanches observed in the Mt Rainier area above treeline.

A frontal system brought 2-3 inches of snow at higher NWAC stations west of the crest Friday night. The new snow was reported to have bonded well to the previously moist surface. Mt. Baker picked up another inch of water Sunday and Sunday night with snow levels 5-6000 ft while other locations experienced fair weather. Monday saw fair and mild weather with more snowpack settlement. 

Snow levels fell quickly after a front moved through early Tuesday morning. Scattered showers through Tuesday afternoon had deposited a few inches near and above treeline along with moderate westerly transport winds. In many areas the old moist surface should be slowly re-freezing with the new snow generally bonding well, keeping avalanche concerns confined to new storm snow layers.  

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.