Avalanche Forecast

Archived

Jan 31st, 2023–Feb 1st, 2023

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

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, North Rockies, Blue River, Clearwater, McBride, Premier, Quesnel, Sugarbowl, Clemina, North Monashee, McGregor, Renshaw, Robson.

Stormy conditions continue with localized enhanced snowfall amounts. New storm slabs will build over a complex snowpack increasing the likelihood of triggering large, destructive avalanches over the coming days.

Confidence

Moderate

Avalanche Summary

Natural avalanche activity is expected on Wednesday due to new snow combined with blowing ridgetop wind.

One natural wind slab size 2 was reported on Monday at 2200 m.

Last weekend, several very large (size 3 to 4) avalanches were triggered naturally on the basal facets. The avalanches were on all aspects and generally in alpine terrain between 2400 and 2900 m. See here for a video of a rider-triggered avalanche near Renshaw and another example here near Clearwater.

These avalanches are similar to what we've seen over the past week, with persistent and deep persistent avalanches releasing on all the weak layers described in the Snowpack Summary. Most avalanches over the past week were large to very large (size 2 to 4), occurring between 1700 and 2400 m and on all aspects. See this MIN for a recent example and see here for information on a fatal skier-triggered avalanche incident from last week near Revelstoke.

See more on the potential of triggering deeper weak layers Forecasters' Blog.

Snowpack Summary

25 cm of new snow and strong westerly wind will form new and reactive storm slabs and wind slabs in lee terrain features. They will overly previously wind-affected snow from recent northeast wind.

Two layers of surface hoar crystals and/or a melt-freeze crust may be found around 30 to 80 cm deep. Surface hoar is most likely found in wind-sheltered terrain around treeline and lower alpine elevations. The melt-freeze crust is found up to 1800 m on all aspects and into the alpine on sun-exposed slopes.

Large and weak facets from November are near the base of the snowpack, which continue to produce very large avalanches in the region.

Weather Summary

Tuesday Night

Cloudy with snowfall, accumulation 10 to 20 cm with local enhancements expected. Ridgetop winds moderate from the West. Treeline temperature -12 °C.

Wednesday

Cloudy with snowfall, accumulation 10 to 20 cm with local enhancements possible. Ridgetop wind light to moderate from the southwest. Treeline temperature -10 °C.

Thursday

Cloudy with snowfall, accumulation 10 to 20 cm with local enhancements possible. Ridgetop wind moderate from the southwest and temperatures near -10 °C.

Friday

Cloudy with snowfall, accumulation 5 to 10 cm. Ridgetop wind light from the southwest. Treeline temperatures warming to -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Avoid all avalanche terrain during periods of heavy snowfall.
Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
Be mindful that deep instabilities are still present and have produced recent large avalanches.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.