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Avalanche Forecast

Archived

Feb 21st, 2015–Feb 22nd, 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.
Below Treeline
Natural avalanches unlikely.

Regions

Snoqualmie Pass.

Watch for new wind slab on non-traditional westerly aspects especially as you increase in elevation and reach into the alpine Sunday.

Detailed Forecast

Moderate easterly winds at crest level and in the Passes should lessen Sunday afternoon. Temperatures will warm a few degrees over Saturday, especially in the alpine with high pressure moving into the region.

Watch for new wind slab on non-traditional westerly aspects especially as you increase in elevation and reach into the alpine where there has been more recent snow available for transport. E-NE winds should continue to build new wind slab Saturday night and Sunday morning. There may also be pockets of lingering wind slab on other aspects as well.  

Small loose wet avalanches will be localized to steeper solar slopes near and above treeline and where wind effects are minimal. 

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 lead to generally thick surface crusts and further consolidation of the snowpack, as well as further deterioration of the snow cover below treeline.

A few weather disturbances passed through in NW flow aloft the latter half of the week, bringing a welcome few inches of snow near and above treeline; the Paradise weather station recorded 8 inches over 2 days ending Saturday morning. Winds veered to the east or northeast on Saturday, causing some new wind slab formation on non-traditional westerly aspects mainly above treeline.  

On Saturday, NWAC observer reports from the Crystal Mt backcountry described a few inches of new snow bonding well to the old surface and minimal wind transport through mid-day. However, at Winchester Mt in the Mt. Baker area, new wind slab 10 - 40 cm thick was observed by program director Scott Schell above treeline on multiple aspects with new NE wind transport in progress. Little loose wet activity was observed in either location with the cold temperatures and wind.   

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.