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Avalanche Forecast

Archived

Jan 4th, 2020–Jan 5th, 2020

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

Regions

Northwest Inland.

There is some uncertainty as to how the recent storm snow is bonding to the old surface and how buried weak layers have reacted under the new load. 

Are you going out in the mountains this weekend? Let us know what you see via the Mountain Information Network!

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Saturday night: Flurries accumulating 10-15 cm, strong southwest wind, alpine high temperatures around -8 C.

Sunday: Flurries accumulating 5-10 cm, moderate west wind, alpine high temperatures around -12 C.

Monday: Mix of sun and cloud with isolated flurries, light southeastt wind, alpine high temperatures around -10 C.

Tuesday: Mix of sun and cloud with isolated flurries, light variable wind, alpine high temperatures around -10 C.

Avalanche Summary

A widespread avalanche cycle up to size 3 was reported from the Howson range during the storm on Friday. This cycle is likely to have occurred throughout the southern part of the region where more than 40 cm of snow fell on Friday. 

Before the storm, reports of persistent slab avalanches associated with buried surface hoar were trickling in, from Ashman, Telkwa and Howson areas. They included natural and artificially triggered avalanches ranging in size from 1.5-3, and have occurred on all aspects mainly at treeline but also in the alpine. The new snow load will increase the size and consequences of avalanches on these layers.

Snowpack Summary

Flurries overnight and into Sunday will bring storm snow depths to 40-50 cm. In the alpine, the storm snow has likely been highly wind affected. Expect to find deep wind loaded pockets below ridgetops and the lee sides of exposed features. Below treeline, soft, unconsolidated snow can be found at low elevations amid cool temperatures.

A couple of layers of surface hoar are now buried 50-100 cm below the surface in sheltered areas around treeline. Reports of avalanche activity on these layers suggest they have recently become active, and the new snow load will provide additional stress.

Terrain and Travel

  • Closely monitor how the new snow is bonding to the old surface.
  • Give the new snow several days to settle and stabilize before pushing into bigger terrain.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

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.

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.