Avalanche Forecast

Archived

Dec 23rd, 2018–Dec 24th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Cariboos.

The persistent slab problem is best managed with patience and conservative terrain choices. Read more in the new forecaster blog here.

Confidence

Moderate - Due to the number of field observations.

Weather Forecast

SUNDAY NIGHT: Scattered flurries with localized accumulations of 3-8 cm, light wind from the southwest, alpine temperatures drop to -10°c. MONDAY: Mostly cloudy with isolated flurries, light wind from the south, alpine high temperatures around -7°c. TUESDAY: Mostly cloudy, light wind, alpine high temperatures around -10°c. WEDNESDAY: Mostly cloudy, light wind, alpine high temperatures around -12°c.

Avalanche Summary

No recent avalanches have been reported, but evidence of a natural avalanche cycle was reported on Friday. Numerous large (size 2) storm slabs and wind slabs were reported, primarily on north and east aspects. Larger persistent slab avalanches (size 3) were also reported on all aspects, a few even destroying mature trees. The persistent slabs were 50-150 cm thick and likely failed on the early December weak layer. Over the past week numerous large natural and human triggered avalanches (size 2-3) have been reported, several of which were triggered remotely (from a distance). A notable human triggered size 2.5 avalanche occurred on a northeast facing slope in Allan Creek last weekend. See details in this MIN report.

Snowpack Summary

Strong wind from the southwest has formed wind slabs in the alpine and around treeline. Stormy weather over the past two weeks has deposited 80-120 cm of snow above a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects) that formed during the dry spell in early December. This layer has been responsible for large persistent slab avalanches, particularly on north and east facing slopes above 1900 m. The potential exists for smaller avalanches to step down and trigger this deeper layer, resulting in very large avalanches. Another weak layer from mid-November is now buried up to 150 cm, but has been less active recently. At the base of the snowpack is a crust that formed in late October. The probability of triggering these deeper layers is low, but the most suspect areas would be steep rocky alpine features with a shallow snowpack.

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.