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Avalanche Forecast

Archived

Feb 5th, 2023–Feb 6th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
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, Blue River, Clearwater, McBride, Premier, Quesnel, Sugarbowl, Clemina, North Monashee, Renshaw, Robson.

Southwest winds and warm temperatures are promoting slab cohesion and building reactive storm slabs in lees. Be especially cautious as you transition into wind-affected terrain and remember that if triggered storm slabs in motion could step down to deeper weak layers and result in very large avalanches.

Confidence

Moderate

Avalanche Summary

On Saturday, a few small windslab avalanches were reported to be reactive to skier traffic at treeline. A natural wind slab avalanche, size 2, was reported on an east aspect at 2100 m.

On Friday, numerous natural wind slabs were observed throughout the region (size 2-2.5). A few large natural deep persistent slabs were also observed in the alpine and treeline (size 2.5-4).

On Thursday, several natural and human-triggered storm and wind slabs were observed up to size 1.5. One large (size 3) deep persistent slab was observed on a north aspect in the alpine.

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 1700 and 2900 m. See here for a video of a rider-triggered avalanche near Renshaw and another example here near Clearwater.

High-consequence avalanche activity is ongoing for the past week. Your best defence is to stay diligent in choosing low-consequence terrain away from overhead exposure.

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

Snowpack Summary

50-90 cm of recent low-density storm snow has blanketed the region. Strong southwesterly winds and warming temperatures continue to build reactive storm slabs. This storm snow sits above a plethora of old snow surfaces including previously wind-affected snow at upper elevations, a sun crust on steep solar aspects, faceted snow, and surface hoar crystals in wind-sheltered terrain.

In the upper meter of the snowpack sits two layers of surface hoar crystals and/or a melt-freeze crust. The surface hoar is most likely found 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

Sunday Night

Mainly cloudy with clear periods and isolated flurries, trace accumulation. Alpine temperatures reach a high of -5 °C. Ridge wind northwest 25 km/h gusting to 65 km/h. Freezing levels fall to 500 m.

Monday

Mainly cloudy with isolated flurries in the afternoon, 2-7 cm accumulation. Alpine temperatures reach a high of -4 °C. Ridge wind southwest 40-60 km/h. Freezing level 1400 metres.

Overnight 5-10 cm accumulation, up to 15 cm in localized areas.

Tuesday

Cloudy with flurries, 5-10 cm of accumulation. Alpine temperatures reach a high of -4 °C. Ridge wind southwest 20-40 km/h. Freezing level 1500 metres.

Wednesday

Mix of sun and cloud with the possibility of light flurries, trace accumulation. Alpine temperatures rise to -7 C. Ridge wind west 20 km/h. Freezing level rises to 900 meters.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • 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.