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Avalanche Forecast

Archived

Jan 4th, 2021–Jan 5th, 2021

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

Regions

Lizard-Flathead.

Human triggered avalanches are likely at higher elevations after a storm crosses the region Monday night.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Frontal systems cross the region Monday night and Wednesday afternoon.

MONDAY NIGHT: 10-20 cm of snow, moderate southwest wind, treeline temperatures around -4 C.

TUESDAY: Flurries easing off in the afternoon then some sunny breaks in the afternoon, moderate west wind, treeline temperatures around -6 C.

WEDNESDAY: Scattered flurries throughout the day with 5-10 cm of snow, light southwest wind, temperatures around -4 C.

THURSDAY: Another 5-10 cm of snow by the morning then clearing in the afternoon, light northwest wind, temperatures around-6 C.

Avalanche Summary

The storm over the weekend resulted in a widespread cycle of storm slab avalanches in the Fernie area. This included numerous size 2-3 explosive and naturally triggered avalanches. There was also persistent slab avalanche on Sunday that was remotely triggered in a north facing gully around 1350 m (see the photo here). The avalanche failed on a 50 cm deep surface hoar layer, and illustrates how the current persistent slab problem is lingering in isolated areas.

Watch for fresh storm slabs on Tuesday and keep in mind the potential for surprisingly large avalanches due to the isolated persistent slab problem.

Snowpack Summary

A brief storm crossing the region on Monday night will bring 10-20 cm of snow and southwest wind to create a new storm slab problem at upper elevations. This is falling on top of 30 cm of settled snow from a few days ago. A melt-freeze crust beneath this snow has been reported up to an elevation of 1900 m, but does not seem to be a problem at this point. Around 50 to 100 cm deep, weak layers of feathery surface hoar and/or faceted grains may overly a hard melt-freeze crust. This layer appears to be bonding in certain areas of the region but remains suspect where it is well preserved.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be careful to keep storm day fever from luring you out into bigger terrain features.
  • Choose slopes that are well supported and have limited consequence.

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.