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Avalanche Forecast

Archived

Feb 27th, 2023–Feb 28th, 2023

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, 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, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

Extensive reports of heavy sluffing and touchy storm slabs have resulted from the storm, even with limited observations and conservative terrain selection. Stick to low consequence slopes while the new snow settles and put your guard way up if the sun pokes out on Tuesday. This is most likely in the north of the region.

Confidence

High

Avalanche Summary

It was a busy day for avalanche activity in the region with almost all operators reporting some variation of the theme of a natural and skier-triggered avalanche cycle as 40-70 cm of new snow settled into touchy storm slabs in some areas and produced powerful dry loose releases where slabs hadn't quite formed. Savvy terrain use kept most releases small, however large audible avalanches are peppered throughout Sunday's reports.

Clear skies last week allowed for observations of many deep persistent slab avalanches as well as explosive control missions, which produced large to very large (size 2 to 3.5) avalanches. They were on all aspects and between 2200 m and 2800 m in elevation. Although many of the avalanches occurred in unrideable terrain, they are evidence that the weak basal snowpack is still triggerable. Riders should continue to avoid thin snowpack areas, which are often found near ridgelines.

Looking forward, storm slabs from the weekend may remain sensitive to human triggering a bit longer than usual, owing to the weak faceted snow they overlie. Otherwise we expect surface instabilities to gradually become more focused toward wind loaded areas.

Snowpack Summary

Stormy conditions over the weekend brought up to about 40-80 cm of new snow to the Monashees, closer to 20-50 cm in the Selkirks, along with strong southwest wind. The new snow buried an interface from the recent cold period which includes faceted (sugary) surface snow, small surface hoar in sheltered areas, and widespread heavy wind effect and wind slabs in exposed terrain from recent northeast winds. Below this interface is 20-50 cm of older storm snow from the beginning of last week.

Around 100 to 130 cm of snow may now rest on a small layer of surface hoar crystals that was buried mid-February. This layer is most likely found around treeline elevations in areas sheltered from the wind. This layer generally appears to be dormant now but could still be capable of producing avalanches in isolated areas. The remainder of the mid-snowpack is generally strong.

A layer of large and weak facets that formed in November is deeply buried, found near the base of the snowpack. The likelihood of human triggering this layer is currently low given its depth. However, it is still best to avoid steep, thin, rocky slopes near ridges at alpine and upper treeline elevations.

Weather Summary

Monday night

Mainly cloudy with isolated flurries. Light southeast winds.

Tuesday

Mainly cloudy with isolated flurries. Light east or southeast winds. Treeline high temperatures around -8 °C.

Wednesday

Cloudy with isolated flurries, increasing overnight. Light west winds shifting southwest and increasing. Treeline high temperatures around -8.

Thursday

Cloudy with continuing snowfall bringing 10-25 cm of new snow, greatest in the north of the region. Moderate southwest winds. Treeline high temperatures around -7.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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 Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.