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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

South Rockies.

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-25 C. 

Sunday: Mix of sun and cloud, light northeast winds, alpine high temperature -8 C. 

Monday: Mostly clear, light variable winds, alpine high temperature -1 C, freezing level 1300 m. 

Tuesday: Mostly clear, light northeast winds, alpine high temperature 0 C, freezing level 1800 m.

Avalanche Summary

Numerous small (size 1-1.5) wind slabs were reported on Saturday failing both naturally and from human and explosive triggers. 

In the aftermath of the previous storm, there were reports of large (size 2-2.5) explosive-triggered avalanches releasing 20-30 cm deep. In a few cases in the neighbouring Lizard Range and Flathead region, these avalanches were triggered by cornice falls.Cornices have grown large with the recent weather, and a cornice failure could trigger a large slab avalanche on the slope below. 

Snowpack Summary

Snowfall totals varied across the region, with some areas accumulating 10-20 cm of snow. Strong easterly winds drifted the new snow into wind slabs on lee terrain features in a reverse-loading pattern.

A total of 25 to 45 cm of snow from the previous storm has been redistributed by wind or is well-settled. This snow sits on older wind slabs in exposed areas, and a sun crust on solar aspects (south through west facing slopes). Melt-freeze crusts extend up to about 1900 m on other aspects. 

A thick crust/facet layer currently sits 40-80 cm below the surface and can be found up to 2100 m. The middle of the snowpack is generally strong, but the base of the snowpack contains 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.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.