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Avalanche Forecast

Archived

Feb 10th, 2022–Feb 11th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

Warm and sunny conditions are keeping the danger elevated. Weak cornices, old wind slabs, and loose wet avalanches should be expected on Friday.

The biggest concern remains a weak layer down 20-70 cm which is still capable of producing very large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A ridge of high pressure brings very warm and sunny conditions which are expected to persist until the end of Sunday. 

Thursday night: Clearing overnight, moderate NW wind , freezing levels around 2000 dropping to near valley bottom overnight.

Friday: Sunny, light N wind, freezing levels climbing to around 2500 m. 

Saturday: Sunny, light variable wind, freezing levels 2500-3000 m with an inversion.

Sunday: A mix of sun and cloud, light to moderate SW wind, freezing levels 2500-3000 m with an inversion. 

Avalanche Summary

No new avalanches were reported on Wednesday but snowballing and pinwheels were observed on solar aspects in the alpine and all aspects at elevations below 1900 m suggesting the upper snowpack became weak with the warm temperatures and sun. 

On Sunday, several skier-triggered avalanches occurred in the region. See reports here, here, and here. Although the St Jacob's slide looks to have been a wind slab, it may have run on the same persistent weak layer associated with other recent avalanches in the region. The Allison Pass avalanches seem more definitively associated with this layer. Each highlights the challenging risk management scenario we're currently in.

On Saturday, a fatal avalanche occurred in the Duffey Lake area. This avalanche was a very large (size 3), skier triggered avalanche with significant propagation. It was triggered at upper treeline on a northeast aspect and it failed on a shallower layer of surface hoar before stepping down to the weak layer from late-January. A more detailed report can be found here. This layer was also responsible for several large skier triggered avalanches in the neighbouring Sea to Sky region.

Snowpack Summary

Warming temperatures and recent light rain has moistened the surface on all aspects and elevations. Formation of surface crust began Wednesday night and is expected to continue Thursday night with clear skies in the forecast. Prior to the warming and rain, strong winds had caused extensive wind effect and wind slab formation in exposed terrain at higher elevations.

The primary concern in the snowpack is the late-January weak layer down 20 to 70 cm. This layer is primarily composed of a crust and facets, but also may include surface hoar in more sheltered areas around treeline elevation. The interface is most prominent at treeline and above in the north of the region. It has been found on all aspects in the Duffey Lake area. This layer is up to about 90 cm deep in the south of the region and has been giving similar, moderate to hard, sudden results in recent snowpack tests but has not produced the same widespread avalanche activity like in the north of the region. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Extra caution is needed around cornices under the current conditions.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.

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.

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.