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Avalanche Forecast

Archived

Feb 25th, 2021–Feb 26th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Cariboos.

The snowpack is currently complex and there have been some large human-triggered avalanches recently. It is important to continue to choose conservative terrain as signs of instability may not be obvious.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Forecast snowfall amounts are uncertain.

Weather Forecast

THURSDAY NIGHT - Flurries, 5-10 cm / moderate to strong southwest wind / alpine low temperature near -12 

FRIDAY - Mainy cloudy with flurries, 5 cm / moderate northwest wind / alpine high temperature near -11

SATURDAY - A mix of sun and cloud with a few flurries / moderate west wind / alpine high temperature near -11

SUNDAY - Mainly cloudy with scattered flurries, 5 cm / strong southwest wind / alpine high temperature near -6 / freezing level 1600 m

Avalanche Summary

Observations from McBride and Valemount areas show evidence of a widespread natural avalanche cycle that took place during the recent storm. 

Several natural and human-triggered avalanches size 2-3.5 were reported on Tuesday near Valemount at alpine and treeline elevations. At least one of the very large human-triggered avalanches was initiated from a wind-loaded start zone at the top of a large alpine feature, propagated for hundreds of meters along a ridge, and ran to valley bottom. Thankfully the rider was able to escape unharmed.

On Tuesday, there was a fatal avalanche just outside of the region, northeast of Valemount in Swift Creek. The avalanche was a size 3.5 and is suspected to have failed on the late January persistent weak layer. The report can be found here.

Snowpack Summary

The region has received 40-80 cm of fresh snow in recent days. There are wind deposits up to 100 cm deep in lee features at upper elevations. The recent snow sits on faceted, and/or previously wind-affected snow that formed on the surface during the extended cold, dry period. 

There is now 80-180 cm of snow above the early February persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features such as cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust. 

A persistent weak layer from late January exists down 90-200 cm. There have been very few recent reports of avalanches or reactive test results on this layer, however, there have been several large avalanches on this layer in the neighboring North Rockies region in recent days, so it is worth keeping in mind.

Terrain and Travel

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Be especially cautious as you transition into wind affected terrain.

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.