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Avalanche Forecast

Archived

Jan 16th, 2023–Jan 17th, 2023

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

Regions

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir.

Another reactive weak layer has reached its tipping point and is producing large human triggered avalanches. The problem is especially prevalent at mid elevations. Put your guard up around steep openings in the trees and keep it raised if you reach the alpine, where an even deeper snowpack weakness remains in play.

Confidence

Moderate

Avalanche Summary

Several more observations of recent persistent slab releases were observed on Sunday in the Norns and the Bonningtons. Two skier-triggered avalanches were also reported. Failure planes in all of these avalanches were identified as the early January layer discussed in our snowpack summary. 1700-2100 m was again the critical elevation band and east to northeast aspects figured prominently.

A widespread and reactive storm slab was reported around the region Friday and into Saturday. Skiers, vehicles, and explosives triggered slabs to size 2.5 with most crowns 30-50 cm deep, and many reported at treeline elevations 1700-2100 m (note poor visibility and no alpine observations). These avalanches were reported failing on the most recent interface or the early January crust/surface hoar layer about 10 cm lower. Wet loose avalanches were observed in below treeline terrain.

On Saturday and again on Sunday, explosives triggered a large (size 2.5) deep persistent slab avalanche (Saturday's report was from the western side of the Forecast region, which has received a bit more storm snow over the weekend, while Sunday's was in the Bonningtons). Both avalanches indicate our deep persistent layer remains reactive to large triggers at least.

Please continue to share any observations or photos on the Mountain Information Network.

Snowpack Summary

Upper elevation storm snow totals since January 12 vary from 20-35 cm. This overlies a rain crust at lower elevations where recent precipitation fell as rain with freezing levels exceeding 1900 m. It overlies a mix of wind-affected and sheltered low density storm snow above about 1700 m.

At higher elevations, 50-60 cm of snow now sits on a layer of surface hoar from the start of January in wind-sheltered terrain, primarily around treeline. It has been identified as the failure plane in many recent avalanches in the region.

Another facet/crust layer is down 40-90 cm (and 2-10 cm thick at TL elevation). Below this the mid-pack is settled and consolidated.

A concerning and weak layer facets and crust 20-50 cm thick makes up the basal snowpack. Treeline snow depths average 150-210 cm.

Weather Summary

Monday night

Cloudy with very isolated flurries. Light west or northwest winds.

Tuesday

Mainly cloudy. Light west winds. Treeline high temperatures around -4 C.

Wednesday

Cloudy with increasing flurries bringing less than 5 cm of new snow, continuing overnight. Light south winds. Treeline high temperatures around -4 C.

Thursday

Decreasing cloud and easing flurries with about 5 cm of new snow from the overnight period. Light northwest winds. Treeline high temperatures around -4 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

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.