Avalanche Forecast

Archived

Feb 9th, 2022–Feb 10th, 2022

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

The weather might feel like spring, but the snowpack isn't there yet. A dangerous persistent weak layer is in play and it is not typical for our region. Warming will increase the chances of destructive avalanches on this layer.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

Wednesday night: Mainly clear. Moderate to strong west winds. Freezing levels remaining near 3300 metres.

Thursday: A mix of sun and cloud. Moderate to strong west winds. Treeline high temperatures around +1 with freezing levels around 2000 metres, falling overnight.

Friday: A mix of sun and cloud. Light north winds. Treeline high temperatures around +1 with freezing levels rising from surface to 2500 metres, remaining elevated overnight.

Saturday: Sunny. Light northeast winds. Treeline high temperatures around +4 with freezing levels to 2700m, remaining elevated overnight.

Avalanche Summary

Several more skier triggered avalanches occurred in the region on Sunday. 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.

Another near miss associated with our late January persistent weak layer occurred in the area of Spectrum Peak, near Rainbow Mountain (Sea to Sky) on Sunday. At least three large avalanches with 1-2 metre crown fractures were remotely triggered by a group of hikers. Fortunately no one was caught. Wind loading at the start zone may account for fracture depths that exceed the typical burial depth of the suspected weak layer.

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 crust from late January referred to above and discussed in our snowpack summary. 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.

We anticipate a significant increase in the likelihood of avalanches on this layer during the warming pattern from Wednesday onward.

Snowpack Summary

Warming temperatures and light drizzle has likely moistened the surface on all aspects and elevations. A trace of new snow preceded the warming, doing little to bury heavy wind effect and wind slabs resulting from recent south winds. Formation of new surface crust may occur in open areas where radiative cooling occurs overnight. Any crust that does form should deteriorate with daytime warming.

The primary concern in the snowpack at present is the 20 to 70 cm of snow from the past week that is sitting above a variety of surfaces including facets and crust, but also surface hoar in more sheltered areas at mid-elevations. This layer is most prominent at treeline and above. 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.

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
If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
Good day to make conservative terrain choices.

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.

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.