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Avalanche Forecast

Archived

Dec 4th, 2021–Dec 5th, 2021

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

Regions

Purcells.

A few tricky layers plague the Purcell snowpack. Approach avalanche terrain with a conservative mindset as the best riding areas may overlap with the greatest avalanche hazard.

Confidence

Low - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

SATURDAY NIGHT: Mostly cloudy with isolated flurries. West-northwest wind, 25-45 km/hr. Alpine low temperature -15 C. Freezing level valley bottom. 

SUNDAY: Mix of sun and cloud. Northwest-west wind, 20-30 km/hr. Alpine high temperature -7 C. Freezing level valley bottom. 

MONDAY: Partly cloudy with isolated flurries and sunny breaks. Variable wind 10-20 km/hr. Alpine high temperature -9 C. Freezing level valley bottom. 

TUESDAY: Mix of sun and cloud. Southwest wind 10-15 km/hr. Alpine high temperature -12 C. Freezing level valley bottom.

Avalanche Summary

Two MIN reports (MIN 1 and MIN 2) on Friday, Dec 3 from Quartz Creek report a deep persistent avalanche failing at the base of the snowpack sometime in the middle of the day. While its unknown if the images MIN 2 cover the same rider-triggered avalanche avalanche reported in MIN 1, they certainly highlight weak and reactive snow at the base of the snowpack.

On Thursday, Dec 2 evidence of a natural avalanche cycle to size 3 occurring overnight Wed-Thurs was observed around the Golden area and north end of the forecast region. Through the day (and throughout the region), large storm slabs (size 2) and large deep persistent slabs (size 2-2.5) were triggered by explosives.

On Wednesday, Dec 1 a natural avalanche cycle was observed near Golden, including storm slabs and cornice failures to size 2 in north facing terrain. Explosive control work also produced several storm slabs. Nearby Glacier National Park observed a widespread natural avalanche cycle and produced up to size 3.5 avalanches with explosive control methods. 

Of note, several recent avalanches in the Toby Creek drainage are thought to have failed on a late November surface hoar layer. This is believed to be lurking around the Toby Creek drainage area, however data is sparse this early in the season and this layer may extend to other areas.

Snowpack Summary

5-30 cm low density snow sits over a supportive crust at upper elevations. Below 1900 m the snow surface turns into a solid crust.

Around the Toby Creek drainage, a surface hoar layer sits down 30 to 60 cm in sheltered features at treeline and below. In a snowpack test on Friday, Dec 1 this layer was observed down 50 cm and showed propagation propensity. We have limited knowledge of the distribution of this layer, but suspect is its most active between 1900-2400 m.  

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been recently reactive to skiers, explosives and reactive in snowpack tests, and will likely continue to be a layer of concern.

Average snowpack depth at treeline is 100-180cm, with the deepest snowpack found near the Bugaboos. 

Terrain and Travel

  • Be alert to conditions that change with elevation and wind exposure.
  • Carefully monitor the bond between the new snow and old surface.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • In times of uncertainty conservative terrain choices are our best defense.

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.

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.

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.