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Avalanche Forecast

Archived

Mar 18th, 2022–Mar 19th, 2022

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

Regions

Cariboos.

Buried weak layers are keeping danger ratings elevated, particularly in the southern half of the region.

Watch for signs of instability like whumpfing, natural avalanches and cracking.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

FRIDAY NIGHT: Partly cloudy, with flurries. Freezing levels drop to 800 m. Light to moderate southwesterly winds. 

SATURDAY: A mix of sun and cloud. Flurries continue, around 5 cm of snow. Freezing levels rising to 1500 m. Moderate southwesterly winds. Alpine high of -1.

SUNDAY: Around 5 cm overnight. Mostly sunny with moderate northwest winds. Freezing levels reach 1200 m, alpine high of -3. 

MONDAY: Scattered flurries with cloudy skies. Moderate southwest winds. Freezing levels reach 1500 m. 

Avalanche Summary

On Thursday, natural avalanche activity was observed up to size 2 in alpine features near Valemount. Storm snow was reactive to human triggers, producing avalanches up to size 1. 

On Wednesday, natural and human triggered activity was observed to size 2 in wind loaded features. Avalanches were naturally and remotely triggered (from a distance), and mostly occurred on south facing slopes around treeline. However of note, a size 3 was remotely triggered on a northeast aspect near McBride. While the layer of concern is only 40 cm deep, this produced a large avalanche with impressive propagation. 

On Tuesday numerous natural and human-triggered storm slabs were reported. These mainly occurred on north-facing (shaded) aspects in the alpine and treeline and failed on a buried weak layer of surface hoar. 

Snowpack Summary

Up to 70 cm of recent settling storm snow sits over a layer of weak surface hoar in sheltered and shaded terrain, and over a crust on south facing slopes. The new snow is bonding poorly to this old surface, producing propagating results on testing and large avalanches within the last 3 days. 

At higher elevations consistent southwest winds are creating deeper deposits on north through east facing features. Below 1300 m, moist snow or a melt-freeze crust likely exists from recent rain and warm temperatures.

The lower snowpack is generally well-settled and strong in most areas, with crust layers 50 to 100 cm deep.

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.