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Avalanche Forecast

Archived

Dec 18th, 2021–Dec 19th, 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 unlikely, human triggered possible.
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

Cariboos.

Touchy storm slabs that formed on Saturday will remain reactive to human triggers through the weekend; especially in wind affected terrain.

The new snow will increase the likelihood of triggering the persistent slab problem. Learn more HERE.

Confidence

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

Weather Forecast

SATURDAY NIGHT: Flurries; 3-5 cm / Light northwest wind / Low of -19

SUNDAY: Clearing skies with a mix of sun and cloud / Light north wind / High of -16

MONDAY: Mix of sun and cloud / Light west wind / High of -17

TUESDAY: Increasing cloudiness with flurries; 3-5 cm / Strong west wind / High of -14

Avalanche Summary

Fresh storm slabs formed on Saturday will likely remain reactive to human triggers through the weekend, especially in wind affected terrain.

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

15-25 cm of new snow and strong southwesterly winds on Saturday formed touchy storm slabs that will remain reactive to human triggers though the weekend; especially 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

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • 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.