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

Snoqualmie Pass.

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 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.

A few weather disturbances passed through last Thursday and Friday, bringing a welcome few inches of snow near and above treeline. Winds veered to the east or northeast on Saturday, causing some new wind slab formation on non-traditional more westerly to southerly 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 through mid-day. However, at Winchester Mt in the Mt. Baker area, new wind slab 10-40 cm thick was observed above treeline on multiple aspects with new NE wind transport in progress. A small loose wet slide was triggered on a south slope late in the day, even with the cold temperatures and wind.

On Sunday, a skier triggered a relatively shallow hard slab in the Nisqually Chutes on Mt Rainer and safely escaped the slide. The slab formed from the recent wind transport Saturday and appears to have formed in a steep terrain feature between rock outcrops. Dallas Glass at Skyline found the 10-15 cm of the most recent snow well bonded near treeline with minimal new wind transport.

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

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.