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Avalanche Forecast

Archived

Jan 9th, 2021–Jan 10th, 2021

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

Regions

Purcells.

Wind slabs will be the most apparent avalanche problem you encounter but keep the potential for persistent slab avalanches in your mind. Avalanche danger may be improving as the likelihood of triggering diminishes but if you're unlucky enough to do so, consequences can be high.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Saturday night: Partly cloudy, light southwest wind at 2000 m, high level wind increasing to moderate west, freezing level valley bottom.

Sunday: Mix of sun and cloud, light southwest wind at 2000 m, high level wind increasing to strong west, alpine high -9, freezing level 600 m.

Monday: Mostly cloudy, light southwest wind at 2000 m, high level wind strong west, alpine high -8, freezing level 1000 m.

Tuesday: Flurries, light southwest wind at 2000 m, high level wind strong west, alpine high -6, freezing level 1200 m.

Avalanche Summary

Some solar triggered loose snow avalanches up to size 1.5 were reported on Friday afternoon. A few natural, human and explosive triggered wind slabs size 1-2 were reported across the region in the latter part of the week.

Two human triggered avalanche incidents occurred on Tuesday; a size 1.5 on surface hoar in a northeast facing burn near Glacier National Park (view MIN report here), and a size 2.5 avalanche on an east aspect at treeline in the Lower Holt area, near Golden (view report here). Thankfully there were no injuries.

A notable avalanche from the natural storm cycle that occurred last weekend include a natural size 2.5 deep persistent slab avalanche reported on a north aspect at 2500 m near Invermere.

Snowpack Summary

Variably wind affected surfaces can be found at upper elevations. 40-60 cm of snow sits on facets in the alpine, and a spotty layer of surface hoar that was buried around Christmas treeline and below. 

The mid-December crust and/or surface hoar is now down 90-140 cm. Although there have been no new reports of avalanches on this layer in the last few days, it remains possible to trigger where it is well preserved.

The lower snowpack is characterized by more crusts, the most notable is a rain crust from early November that is near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

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.