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Avalanche Forecast

Archived

Feb 11th, 2023–Feb 12th, 2023

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

North Columbia, South Columbia, Esplanade, Jordan, North Selkirk, Shuswap, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

We're still seeing smaller wind slab and cornice releases triggering the weak basal snowpack as well as other recent persistent layers. It's not a mistake to focus in on wind slab problems, but make sure to factor in the consequences of a larger, more destructive step down avalanche when you're eyeing up surface hazards.

Confidence

Moderate

Avalanche Summary

Among several natural and human triggered wind slabs and storm slabs (as large as size 2.5), Friday's reports also included a few notable observations of step down avalanches. One of these was a cornice release that triggered a small pocket to the basal snowpack in the South Monashees while another report from the central Monashees details wind slabs in several instances stepping down to one of several midpack layers covered in our snowpack summary.

Reports from Thursday included more observations of the natural cycle described below, in addition to several size 1 (small) to size 2 (large) skier-triggered slabs. Size 1's were up to about 20 cm -deep wind slabs while the lone new size 2 north of Trout Lake failed on a 75 cm-deep freezing rain crust buried in early January.

With clearer weather on Wednesday, a widespread avalanche cycle from within the storm was observed across the region. Several persistent slab avalanches were reported between 2200 and 2400 meters on all aspects. Notable was a size 2 vehicle remote persistent slab avalanche, triggered from 70 m away on a northwest aspect. Several deep persistent slabs were reported to size 4 throughout the Selkirks and Purcells. Numerous wind slab and storm slab avalanches were reported to size 3 on all aspects at treeline and above.

Snowpack Summary

Southwest winds have been redistributing storm snow into 20-30 cm soft slabs in exposed alpine and treeline areas. 40-90 cm of storm snow from the week sits above wind-affected surfaces and a crust that extends up to 1800 m in the northern part of the region and up to 2000 m further south. Small facets may be found above the crust. This layer seems like it could be an emerging concern in the southeast of the region.

Deeper in the snowpack two layers of surface hoar which formed in early January are 60 to 120 cm deep. Although snowpack tests are indicating they may be strengthening, these weak layers are still being watched closely by local operators and may be associated with recent isolated step-down avalanches.

Large and weak facets from November are near the base of the snowpack and although avalanche activity on this basal weakness has been on a bit of a decline, it still figures prominently in the assessments and terrain use (and avoidance) of professionals throughout the region.

Weather Summary

Saturday night

Increasing cloud with possible isolated flurries. Light southwest winds.

Sunday

Cloudy with flurries bringing 5-15 cm of new snow by end of day, continuing overnight, with greatest amounts in the north of the region. Light to moderate southwest winds, increasing and becoming strong in the alpine. Treeline high temperatures around -3 with freezing levels to 1300 metres.

Monday

Cloudy with another 10-20 cm of new snow from the overnight period, greatest in the north of the region. Light to oderate southwest winds, easing over the day. Treeline high temperatures around -5.

Tuesday

Cloudy with isolated flurries and up to about 5 cm of new snow, including overnight amounts. Light northwest winds. Treeline high temperatures around -7.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.

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.