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Avalanche Forecast

Archived

Feb 24th, 2021–Feb 25th, 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 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

South Rockies.

Danger will increase as the day progresses with new snowfall and strong wind. Storm slabs, wind slabs, and a buried weak layer could be triggered by riders on Thursday.

Confidence

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

Weather Forecast

WEDNESDAY NIGHT: Increasing clouds, 30 to 60 km/h southwest wind, alpine temperature -12 C.

THURSDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 30 to 60 km/h southwest wind, alpine temperature -10 C.

FRIDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 20 to 40 km/h west wind, alpine temperature -10 C.

SATURDAY: Partly cloudy, 30 km/h west wind, alpine temperature -11 C.

Avalanche Summary

We received a few reports of storm slab avalanches around 30 cm deep on Monday and Tuesday, localized in the south of the region. The MIN here describes natural activity within the storm snow from earlier this week.

Looking towards Thursday, human triggering of storm, wind, and persistent slabs will remain likely. Conditions are not easily managed right now, warranting a conservative mindset!

Snowpack Summary

Stormy conditions will impact the region on Thursday, building on slabs formed earlier this week. Wind slabs are expected to build over the day in exposed terrain at treeline and alpine elevations. Storm slabs may build in sheltered areas at all elevations. These slabs are expected to reach between 20 and 50 cm thick over the region and sit above sugary faceted snow formed mid-February.

Around 50 to 80 cm deep, a weak layer of surface hoar may be found in sheltered terrain or otherwise faceted grains and/or a hard melt-freeze crust. This layer has so far shown to be most problematic around the Elk Valley, but you may find it elsewhere.

Weak faceted grains and a decomposing melt-freeze crust are likely found near the base of the snowpack. There have not been recent avalanche observations on this layer, but steep and rocky slopes as well as shallow snowpack areas should be approached with caution.

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Choose conservative terrain and watch for clues of instability.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • 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.