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Avalanche Forecast

Archived

Mar 14th, 2020–Mar 15th, 2020

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

Regions

Lizard-Flathead.

Strong northeast winds have formed wind slabs on atypical slopes. Sunny skies and a warming trend could start to weaken sun-exposed slopes and cornices.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Saturday night: Decreasing cloud, light northeast winds, alpine temperature -23 C.

Sunday: Mostly clear, light northeast winds, alpine high temperature -8 C. 

Monday: Clear, light northeast winds, alpine high temperature -3 C, freezing level 1300 m.

Tuesday: Mostly clear, light northeast winds, alpine high temperature near 0 C, freezing level 2000 m.

Avalanche Summary

Several large (size 2) wind slabs were reported on Saturday releasing naturally on lee slopes above 1700 m. Numerous small (size 1) wind slabs were also reported as a result of ski cuts.

Cornices have grown large with the recent weather, and a cornice failure could trigger a wind slab avalanche on the slope below. On Friday, there were reports of cornice falls triggering small wind slab avalanches. 

Over the past few days, there have been several reports of natural, human-triggered, and explosive-triggered avalanches releasing in the previous storm snow, primarily on lee aspects above 1900 m. These avalanches were small to large (size 1.5-2), breaking 20-60 cm deep, and in a few cases, triggered by cornice falls.

Avalanches are expected to become more reactive with a significant warm-up forecast for the coming days.

Snowpack Summary

Strong easterly winds have drifted recent snow into wind slabs on lee terrain features in a reverse-loading pattern. A major warming trend is forecast over the next several days, which could rapidly weaken the snowpack and cornices.

A total of 30 to 60 cm of snow from the previous storm has been redistributed by wind or is well-settled. This snow sits over another layer of buried wind slabs in exposed areas and a sun crust on solar aspects (south through west facing slopes). Melt-freeze crusts extend up to 1900 m on other aspects. 

A thick crust/facet layer currently sits 30-60 cm below the surface. There has been only one avalanche reported on this layer since February 17th. The middle of the snowpack is generally strong, but the base of the snowpack contains weak basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.