Avalanche Forecast

Archived

Jan 4th, 2020–Jan 5th, 2020

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 and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Cariboos.

Continuing snowfall and wind is out-pacing the snowpack's ability to adjust. Stay vigilant with simple terrain choices as this pattern continues.

Confidence

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

Weather Forecast

Saturday night: Mostly cloudy, scattered flurries with trace accumulations, moderate to strong southwest winds, alpine temperature -10 C.

Sunday: Cloudy, 5-15 cm of snow, strong southwest winds, alpine high temperature -6 C.

Monday: Mostly cloudy with isolated flurries, light southwest winds, alpine high temperature -6 C.

Tuesday: Cloudy, 10-15 cm of snow, light southeast winds, alpine high temperature -5 C.

Avalanche Summary

On Friday and Saturday there were reports of numerous large (size 2-2.5) storm slab avalanches releasing naturally on all aspects and all elevations. This MIN report from Saturday is a great example. Several avalanches have also been remote-triggered, like this one observed Wednesday.

Within the past week, a couple avalanches reportedly released on deeper buried weak layers. While avalanche activity on these deeper layers has tapered, it is not out of the question given the continual loading from new snow and wind.

Snowpack Summary

50-80 cm of new snow has fallen throughout the past week creating a touchy storm slab problem. At high elevations, this snow has been redistributed by strong southwest winds, loading lee features near ridges and exacerbating reactivity. The storm snow overlies a weak layer of feathery surface hoar and a hard melt-freeze crust on sun-exposed aspects, also increasing the reactivity of these slabs.

There are a couple weak layers buried around 60 to 180 cm deep, including two more layers of surface hoar from December, and a weak facet/crust layer near the bottom of the snowpack from late November buried over 160 cm deep. It is possible that easier-to-trigger storm slab avalanches could step down to these deeper, persistent layers or that the weak layers could be human-triggered in areas in the alpine where the snowpack is thin, rocky, or variable.

Terrain and Travel

Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Be alert to conditions that change with elevation and wind exposure.
Avoid freshly wind loaded terrain features.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.

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.