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Avalanche Forecast

Archived

Jan 27th, 2017–Jan 28th, 2017

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

Regions

Kootenay Boundary.

A complex avalanche hazard exists in our region. Wind slabs may be strengthening, but the persistent slab problem will linger much longer. Thin snowpack areas such as the Rossland Range are especially concerning.

Confidence

Moderate - Freezing levels are uncertain on Saturday

Weather Forecast

Friday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light to moderate from the west. Freezing level to 1000 metres with alpine temperatures of -7. A temperature inversion may bring alpine temperatures to +2.Saturday: Cloudy with sunny periods. Winds light to moderate from the west. Freezing level to 1100 metres with alpine temperatures of -2. A temperature inversion may bring alpine temperatures to +2.Sunday: Cloudy with sunny periods. Winds moderate to strong from the west. Freezing level to 1300 metres with alpine temperatures of -1. A temperature inversion may bring alpine temperatures to +2.

Avalanche Summary

Aside from small loose snow releases from steep terrain, no new avalanches have been reported.While the reports are rather dated at this point, two recent avalanche involvements remain worthy of consideration. The first, a skier fatality that occurred on Saturday is that it took place on a S/SE facing aspect near 2050m in a cross-loaded feature in the Ymir area. The second report, found on the MIN, details a cornice-triggered Size 2 on Friday near Cabin Peak in the Bonnington range. The initial failure was in the storm slab on a southeast aspect near 2000m but more significantly was observed stepping down to trigger a weak layer deeper in the snowpack. The involvement of deep snowpack weaknesses is keeping these reports in our discussion in spite of their age.(N.B. An error placing Saturday's fatality in the Rossland Range has been corrected)

Snowpack Summary

A complex and tricky snowpack exists in the Kootenay Boundary region. At the surface, a trace to 15 cm of new snow has fallen over the region over Tuesday and Wednesday, covering surface hoar that was previously observed growing up to 6 mm. Combined with Sunday's 3-12 cm and 35-55 cm from last week's storms, the storm snow forming our upper snowpack now totals a rather variable 40-80 cm. The initial snowfall last week was accompanied by moderate to strong southerly winds, resulting in touchy storm and wind slabs forming and bonding poorly to the previous (January 17) snow surface that includes facets and large surface hoar on sheltered slopes and/or a sun crust on steep sun-exposed aspects. This varied layer continues to give easy to moderate and occasionally sudden results in snowpack tests (down anywhere from 30 to 60cms depending on location). In some areas of the Rossland range, the mid-November rain crust / facet layer is now found down 60-100 cm and has proven reactive with recent loading and warming. In thin rocky areas, particularly in the Rossland range, recent reports include easy sudden collapse snowpack test results on facets down 120-150 cm near the ground.

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.

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.