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Avalanche Forecast

Archived

Feb 23rd, 2015–Feb 24th, 2015

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

Regions

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Small loose wet avalanches and lingering but isolated recently formed wind slab will most likely be found above treeline Tuesday. 

Detailed Forecast

Generally light winds and cooling temperatures are expected Tuesday. 

As a result of the cooling, loose wet avalanches should be less likely, but possible in the late morning or near midday, on steeper solar slopes near and above treeline. 

Recent shallow wind slab formed on non-traditional westerly aspects above treeline may still be reactive on specific terrain features. 

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 mild 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 especially further from the crest.

A few weak weather disturbances passed through under NW flow aloft last Thursday and Friday, bringing an inch or two of new snow near and above treeline and near the Cascade crest.

Winds veered to the east or northeast on Saturday, likely causing some very shallow new wind slab formation onto non-traditional westerly to more southerly aspects, mainly above treeline.  

Observations in the Rainy Pass area over the weekend noted shallow wind slabs of 15-25 cm (6-10 inch) forming on SE-S-SW facing slopes, with cracking but no releases observed. Challenging wind crusts were noted on wind exposed northerly aspects above tree line.  Good skiing was found on more sheltered terrain near tree line.

While the January 15th facet/crust layers can still be identified in parts of the NE Cascades, this persistent weak layer has been stabilizing and become unlikely to trigger. As a result the Persistent Slab problem has been removed from the northeast zone.

Problems

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.