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Avalanche Forecast

Archived

Jan 20th, 2021–Jan 21st, 2021

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

Regions

Northwest Inland.

Triggering avalanches remains possible with wind slabs at upper elevations and deep persistent slabs in steep rocky terrain.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

WEDNESDAY NIGHT: Clear skies, light northeast wind, treeline temperatures around -8 C.

THURSDAY: Mostly sunny, light northeast wind, treeline temperatures around -6 C.

FRIDAY: Sunny, light north wind, treeline temperatures around -5 C.

SATURDAY: Increasing cloud during the day, moderate northwest wind, treeline temperatures around -10 C.

Avalanche Summary

Extreme wind on Tuesday resulted in a natural cycle of wind slab avalanches, with rain causing some wet loose avalanches below 1000 m. Natural wind slab avalanches to size 2 were observed over the weekend, and skiers easily cut size 1 slabs on loaded slopes.

Deep persistent slab avalanche activity has been more sporadic (as it often is). A size 2.5 deep persistent slab avalanche was reported from Skilokis over the weekend, that appeared to be triggered by a cornice and failed on a facet/crust layer. Explosives triggered a few size 2.5 persistent slab avalanches near the southern boundary of the region on Jan 7 as well as some very large size 3-4 deep persistent slab avalanches at Ningunsaw in the far north of the region over the past few days. These are reminders of this low-probability / high-consequence scenario.

Snowpack Summary

Another 5-20 cm of snow on Tuesday added to the recent incremental snowfalls. Gusty and variable winds have impacted loose snow and developed slabs in exposed areas. Warm temperatures have produced a crust up to 1000 m and higher on solar aspects. A few isolated surface hoar layers were observed forming over the past weeks and would now be 30-60 cm deep if preserved, but these layers have not been reported in recent snowpack and avalanche observations. The main snowpack feature we are tracking is two crusts in the lower snowpack that have some weak faceted snow around them. Reports from the Smithers area suggest the upper crust is 70-140 cm below the surface and has shown signs of being possible to trigger from shallow areas. The deeper crust is near the bottom of the snowpack and is most likely to trigger from steep rocky slopes (especially in thinner areas like the Babines).

Terrain and Travel

  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.

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.

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.