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Avalanche Forecast

Archived

Jan 5th, 2020–Jan 6th, 2020

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 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? 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

Sunday night: Flurries accumulating up to 5 cm, moderate west wind, alpine temperatures around -12 C.

Monday: Sunny with cloudy periods, light to moderate west to northwest wind, alpine high temperatures around -12 C.

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

Wednesday: Mix of sun and cloud with isolated flurries, light to moderate 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 with avalanches up to size 2 observed below treeline. This cycle is likely to have occurred throughout the southern part of the region on Friday and Saturday, 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

40-60 cm of recent storm snow has been highly wind affected in the alpine. Expect to find deep wind loaded pockets below ridgetops and the lee sides of exposed features. 

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 before the last storm suggest they may be active, especially now that they are under additional snow load.

Terrain and Travel

  • Closely monitor how the new snow is bonding to the old surface.
  • 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.
  • Uncertainty is best managed through conservative terrain choices at this time.

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.