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Avalanche Forecast

Archived

Feb 22nd, 2021–Feb 23rd, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Recently formed storm and wind slabs will likely remain triggerable to riders on Tuesday, as will be the lurking weak layer that has caught many riders in the past few weeks. Conservative terrain travel is recommended!

Confidence

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

Weather Forecast

MONDAY NIGHT: Cloudy with snowfall then clearing, accumulation 10 to 20 cm, 60 km/h west wind, alpine temperature -7 C, freezing level dropping to valley bottom overnight.

TUESDAY: Mix of sun and cloud, 30 km/h west wind, alpine temperature -9 C.

WEDNESDAY: Clear skies, 20 km/h southwest wind, alpine temperature -9 C.

THURSDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 30 km/h southwest wind, alpine temperature -10 C.

Avalanche Summary

Much of the area wasn't visible on Sunday and Monday due to stormy conditions, but many large (size 2) storm slabs were triggered on Monday near Fernie. Extensive natural and human-triggered avalanches were probable across the region during the stormy period. We may see further evidence of the activity as the skies clear on Tuesday.

Snowpack Summary

Around 20 to 50 cm of snow fell on Monday, with the most in the east of the region near the divide. Storm slabs likely developed rapidly. The freezing level hovered around 1600 m, soaking the snowpack below. Strong south to southwest wind dominated, forming new wind slabs in exposed terrain. More snow, strong west wind, and a dropping freezing level are forecast for Monday night, building on these slabs into Tuesday.

All this snow and rain are loading a weak layer found around 50 to 100 cm deep. The layer may consist of weak and feathery surface hoar, sugary faceted grains, or faceted grains associated with a hard melt-freeze crust. Many avalanches in the past few weeks have been triggered on these layers.

There are presently no deeper concerns.

Terrain and Travel

  • Choose conservative terrain and watch for clues of instability.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.