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Avalanche Forecast

Archived

Feb 27th, 2021–Feb 28th, 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.

A complex snowpack can be safely managed by sticking to simple terrain. With persistent slab avalanches, there are often no obvious signs of instability. When triggered, these avalanches are large and destructive. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

SATURDAY NIGHT - Mainly cloudy with flurries, 5-10 cm / moderate southwest wind / alpine low temperature near -14 

SUNDAY - Mainly cloudy with scattered flurries / strong west wind / alpine high temperature near -6 / freezing level 1500 m

MONDAY - Mainly cloudy with flurries, 5 cm / strong southwest wind / alpine high temperature near -6 / freezing level 1500 m

TUESDAY - Mainly cloudy / strong southwest wind / alpine high temperature near -9 / freezing level 1000 m

Avalanche Summary

Multiple persistent weak layers in the snowpack may have reached their tipping point. Avalanches on these layers will be large and destructive. The only way to truly manage this problem is to stick to simple terrain.

There was a report of a natural size 2.5 avalanche running full path in the Dore River area on Thursday. A MIN report about this can be viewed here.

Several natural and human-triggered avalanches size 2-3.5 were reported on Tuesday near Valemount at alpine and treeline elevations. One very large human-triggered avalanche was initiated from a wind-loaded start zone at the top of a large alpine feature. It 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 snowpack in the Cariboos is currently complex, with multiple persistent weak layers.

The region has received 40-90 cm of fresh snow in the past week. There are deep wind deposits in lee features at upper elevations. The recent snow sits on a persistent weak layer of facets that formed on the surface during the early to mid-February cold snap.

There is now 80-180 cm of snow above another persistent weak layer from early February which is composed of surface hoar. This layer is most prevalent at treeline and below treeline. On steep south-facing terrain, this layer may consist of facets on a sun crust. 

Yet another persistent weak layer from late January exists down 90-200 cm. There have been very few recent reports of avalanches on this layer, however, there have been several large avalanches on this layer in the neighboring North Rockies region recently. 

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • 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.
  • Be aware of highly variable recent wind loading patterns.

Problems

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.

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.