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Avalanche Forecast

Archived

Dec 17th, 2021–Dec 18th, 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

Cariboos.

Touchy storm slabs will form throughout the day on Saturday and be most reactive in wind affected terrain. Expect the danger to be HIGH in localized areas that receive greater than 25 cm of snow.

A concerning persistent slab problem exists in much of this region. Learn more HERE

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

FRIDAY NIGHT: Snow; 3-5 cm / Moderate, southwest wind / Low of -19

SATURDAY: Snow; 15-20 cm + 5-15 cm Saturday night / Strong, southwest wind / High of -12

SUNDAY: Clearing skies with flurries; 0-3 cm / Light, north wind / High of -15

MONDAY: Sunny ; Light, southwest wind / High of -17

Avalanche Summary

New snow and wind on Saturday will form touchy storm slabs reactive to human triggers.

A skier triggered size 2.5 persistent slab was reported on Tuesday. This avalanche failed on the crust layer down 40-150 cm. The photo of this avalanche in our recent blog demonstrates the layer's ability to propagate large distances, resulting in large and destructive avalanches.

Snowpack Summary

30-50 cm of recent low density snow has been redistributed by strong northwest winds which are switching to southwest with the incoming storm. 

Forecast snow and wind on Saturday are expected to form touchy storm slabs reactive to human triggers at all elevations, but will be most reactive in wind affected terrain.

Below the new snow, the prominent layer of concern in most of the region is a crust that was formed in early December and is now down 40-150 cm, which is prime depth for human triggering.

This layer has created a persistent slab problem that has recently surprised riders with large avalanches.

Another crust layer near the bottom of the snowpack has not produced any recent avalanches but may be possible to trigger by hitting a shallow spot in the snowpack on a large alpine feature.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

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.