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Avalanche Forecast

Archived

Feb 17th, 2020–Feb 18th, 2020

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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Dig down and investigate the bond between the recent storm snow and old surface snow before committing to big terrain. Be mindful of reactive wind slabs as you move around ridge features and wind-loaded terrain.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Partly cloudy. Alpine low temperature -12 C. Northwest wind 20-30 km/hr.

TUESDAY: Mix of sun and cloud. Alpine high temperature -3 C. North-northwest wind 15-25 km/hr

WEDNESDAY: Sunny. Alpine high temperature -2 C. Northwest wind 15-35 km/hr.

THURSDAY: Mostly sunny. Alpine high temperature -7 C. Southwest wind 10-15 km/hr.

Avalanche Summary

This past weekend a reactive storm slab developed from 20-40 cm fresh snow, with higher snowfall amounts favoring the eastern part of the forecast region. 

On Saturday, storm and wind slab avalanches size 1-1.5 were triggered by skiers, along with loose dry sluffing in steep terrain. In sheltered terrain, avalanches failed on a reactive layer of surface hoar buried by the storm snow. Overnight Saturday and into Sunday, the reactive storm slab produced a size 1-2 natural avalanche cycle. 

Through Sunday, skier traffic and explosives continued to trigger size 1-2 avalanches. Storm slab avalanches were reported at treeline and below, with many reports on northeast to northwest aspects; a layer of surface hoar 20-40 cm is the likely culprit. At treeline and above, naturally failing and skier triggered wind slab avalanches were observed on south and east aspects. 

Snowpack Summary

20-40 cm new snow over the weekend covered a variety of surfaces: hard wind slabs around ridgetops and northerly alpine features, soft slabs and 10-15 cm of lower density snow in sheltered terrain, a thin sun crust on solar aspects, and scoured features in exposed terrain. A reactive layer of surface hoar has been the weak layer in many recent storm slab avalanches around treeline and below. In the alpine west-southwesterly winds have developed reactive windslabs with the touchiest deposits in lee-ward and cross-loaded terrain.  

A thick rain crust to mountain top sits 10-40 cm of below the surface in the east of the region and 40-100 cm in the west. Reports suggest the bond is improving, and the midpack below the crust is wll settled. Weak facet/crust layers near the base of the snowpack have not been an active avalanche problem recently. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.

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.