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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

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.
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.

Recent heavy snowfall means that storm slabs will be widespread and easy to trigger. Don't let the nicer weather lure you into bigger terrain.

Be aware of the potential for solar triggered avalanches. With so much new snow, it may not take much sun to trigger avalanches.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy / light to moderate west wind / alpine low temperature near -11 

THURSDAY - Mainly sunny / light west wind / alpine high temperature near -8 

FRIDAY - A mix of sun and cloud / moderate to strong west wind / alpine high temperature near -5 

SATURDAY - Mainly cloudy / light to moderate southwest wind / alpine high temperature near -8

Avalanche Summary

With the abundant new snow and recent strong to extreme winds, storm slab avalanches will remain easy to trigger on Thursday, especially in wind loaded areas, and on sun-exposed slopes.

There was a widespread natural avalanche cycle with avalanches up to size 3 reported on Tuesday night and during the day on Wednesday. There were also reports of numerous explosives triggered avalanches up to size 2.5, one of which was a persistent slab avalanche.

On Sunday, there were a few explosives triggered persistent slab avalanches to size 2.5. These were reported to have failed on weak facets above a crust that was buried in early December.

On Saturday, explosive testing near Fernie produced several large persistent slab avalanches up to size 2.5 also failing on the early December persistent weak layer.

A couple of large (size 3) naturally triggered persistent slab avalanches were reported on large alpine features last Thursday. These avalanches were triggered by either smaller wind slab avalanches, or cornice falls. These are continued reminders of the "low probability; high consequence" scenario that persistent slab problems often create. 

Snowpack Summary

The region received over 50 cm of new snow between Tuesday night and Wednesday afternoon with strong to extreme westerly winds. Storm and wind slabs are likely widespread and reactive.

Roughly 80-120 cm of snow is now sitting on a crust that extends up to 1900 m. In isolated areas below treeline, this recent snow may be sitting on a weak layer of surface hoar.

The main feature we are monitoring in the snowpack is a layer of weak faceted snow over a hard melt-freeze crust found around 120-200 cm down. Recent sporadic, large, naturally triggered avalanches have occurred on this layer on large alpine slopes and were triggered by either smaller wind slab avalanches, or cornice falls.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.