Avalanche Forecast
Purcells
New storm slabs will continue to build over a snowpack that is rife with deeply buried and reactive weak layers. Keep seeking out simple terrain that is free of overhead hazards.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Choose sheltered terrain where new snow hasn't been wind-affected.
- If triggered, storm slabs may step down to deeper layers and result in very large avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several deeply buried weak layers are persisting in the snowpack and continue to produce very large avalanches, especially with heavy triggers. This is a time to carefully measure your exposure to avalanche terrain and to avoid overhead hazards.
Travel and Terrain Advice
- Seek out low angle, low consequence terrain as well as terrain that has seen heavy traffic.
- Either avoid or space out and travel quickly through runout zones of avalanche paths.
Avalanche Summary
Reports from Friday included observations of ski cutting producing wind slab releases from Size 1-1.5 at higher elevations. One size 2 persistent slab was remotely triggered on a northeast aspect at 1900 metres in the north of the region, failing on the mid-January weak layer down 70 cm. Another report details a size 3.5 persistent slab that released naturally in the past couple of days in the north of the region. This avalanche initiated at 1400 metres and ran to the bottom of its path, producing a 3 metre high deposit of debris.
On Thursday, explosive control work produced slab avalanches up to size 3 on a variety of aspects between 1900 m and 2500 m.
Reports from Wednesday included observations of explosives control in the Bugaboos and surrounding area producing numerous persistent slab results from size 2-3.5. Many of these avalanches ran on the mid-December layer buried 150-200 cm deep. Northwest through northeast aspects in the alpine were the primary targets.
A widespread natural avalanche cycle to size 4.0 was reported on Tuesday, with larger and more frequent avalanches in the north of the region where storm snow totals were higher.
Snowpack Summary
Roughly 10-20 cm of new snow fell over Thursday night and Friday, bringing recent storm snow totals to a rather variable 15-50 cm. This storm snow overlies a complex and generally weak snowpack structure with three active weak layers that we are monitoring:
70-120 cm of snow overlies a crust and/or surface hoar layer (from mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The surface hoar is 10-30 mm in size and exists at all elevation bands.
Deeper in the snowpack (down about 80-130 cm), a persistent weak layer known as the early-January layer is present at all elevation bands, and composed of surface hoar on sheltered slopes and sun crust on steep solar aspects. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential.
Another persistent weak layer that was buried mid-December is 90 to 200 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line and features prominently in recent avalanche reports.
Weather Forecast
Sunday: Cloudy with flurries bringing 5-10 cm of new snow, continuing overnight. Light variable winds. Alpine high temperatures around -7.
Monday: Cloudy with scattered flurries bringing approximately 5 cm of new snow. Light to moderate west winds. Alpine high temperatures of -9.
Tuesday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Moderate west winds. Freezing level rising to 1300 metres with alpine high temperatures of -6.
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Friday's storm formed new storm slabs at all elevations and ongoing snowfall will continue to build and add mass to these slabs. The problem is especially concerning at alpine elevations where strong winds have made slabs extra thick and reactive.