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Avalanche Forecast

Archived

Feb 12th, 2023–Feb 13th, 2023

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

Regions

Cariboos, Blue River, Clearwater, McBride, Premier, Quesnel, Sugarbowl, Clemina, North Monashee, Renshaw, Robson.

Steady snowfall through Monday will continue to form fresh and reactive storm slabs primed for human triggering. This widespread problem will overlap an emerging persistent slab issue recently observed near McBride. Keep in mind that triggering a slab on the surface is probably the most effective way to cause a large and destructive step down avalanche.

Confidence

Low

Avalanche Summary

A revealing MIN post from the McBride area on Saturday showed concerning evidence of an emerging persistent slab problem associated with what is likely our initial storm interface from early February. Aside from easy test results in surface layers, a more problematic layer of surface hoar buried 65 cm deep in this below treeline area appears to be the culprit in numerous touchy persistent slab releases. This activity suggests extra caution is currently needed to manage overlapping storm slab and persistent slab problems.

Snowpack Summary

Another 15-30 cm of new snow is expected to accumulate over higher terrain in the region by end of day Monday, adding to an impressive 80-120 cm of storm snow accumulated over the past week. The latest of this new snow came with strong to extreme southwest winds.

The bond of this recent snow to recent storm interfaces has come into question with a recent observation from the McBride area that suggests a number of active failure planes within and at the base of this storm snow, all of which have given easy to moderate and sudden snowpack test results and very concerning remote triggering below treeline.

Two layers of surface hoar crystals and/or melt-freeze crust sit in the mid-snowpack. The roughly 1 m deep surface hoar is most likely found around shaded treeline and lower alpine elevations. (It may in fact be the 65 cm-deep layer described in the linked MIN post.) The roughly 150 cm-deep melt-freeze crust is found up to 1800 m on all aspects and into the alpine on sun-exposed slopes. These layers continue to be tracked by local operators, but only the surface hoar layer seems like it might currently be an active weak layer.

A final concerning weak layer in the snowpack is composed of large and weak facets from November located near the base of the snowpack. Although this layer hasn't produced avalanches recently, it continues to guide terrain selection by professionals in the region.

Weather Summary

Sunday night

Cloudy with continuing snowfall bringing 10-15 cm of new snow. Strong southwest winds easing in the morning.

Monday

Cloudy with lingering flurries bringing 5-10 cm of new snow. Light to moderate west winds, easing over the day. Treeline high temperatures around -7.

Tuesday

A mix of sun and cloud. Light northwest winds shifting southwest. Treeline high temperatures around -10.

Wednesday

Mainly cloudy. Light to moderate southwest winds. Treeline high temperatures around -8.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Use careful route-finding and stick to moderate slope angles with low consequences.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

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.