Avalanche Forecast

Archived

Jan 18th, 2023–Jan 19th, 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 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

Northwest Coastal, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson, Ningunsaw.

Avalanche danger will increase throughout the day as an intensifying storm brings strong wind and heavy snowfall. Be prepared to dial back your exposure to avalanche terrain and tune in to changing conditions.

Choose conservative, low-consequence terrain as buried weak layers have the potential to produce large and surprising avalanches as active loading continues.

Confidence

Moderate

Avalanche Summary

On Monday, several large (size 2-3) persistent slab avalanches occurred with explosive control in the south of the region. These avalanches failed on a weak facet layer formed in late December.

On Tuesday, several natural storm slabs were observed (size 1-2) from the alpine and treeline. Numerous wet loose avalanches were observed at lower elevations where the precipitation fell as rain.

Looking forward to Thursday, stormy conditions will continue. Riders should expect danger to increase throughout the day as intensifying snowfall builds reactive storm slabs. Avoid wind-loaded areas at upper elevations and keep in mind the potential for deeper instabilities to produce large and surprising avalanches.

Snowpack Summary

Continued snowfall will add to 20-40 cm of recent storm snow. At upper elevations, southerly winds are scouring windward areas and redistributing this storm snow into wind slabs in lee areas. Below 1000 m moist snow or a crust can be found at or near the surface.

A weak layer of surface hoar buried in early January is now down 30-60 cm. This layer is spotty in its distribution and is of greatest concern in sheltered and shaded openings at treeline.

Weak layers that were reactive over the Christmas and New Year's period have shown signs of bonding and gaining strength. These include a surface hoar layer buried on Dec 28 found 50 to 100 cm deep and a facet layer buried on Dec 23 found 70 to 120 cm deep.

Weather Summary

Wednesday night

Cloudy with clear periods and isolated flurries. Alpine temperatures drop to a low of -5 °C. Ridge wind southwest 20 km/h gusting to 65 km/h. Freezing level at valley bottom.

Thursday

Cloudy with snowfall increasing in the afternoon, 5-20 cm of accumulation. Alpine temperatures reach a high of -2 °C. Ridge wind southwest 20 km/h gusting to 70 km/h. Freezing level rises to 600 metres.

Friday

Cloudy with precipitation, 10-15 cm of new accumulation at higher elevations. Alpine temperatures reach a high of 0 °C. Ridge wind southwest 25 km/h gusting to 90 km/h. Freezing level rises to 1300 metres.

Saturday

Mainly cloudy with scattered flurries. Alpine temperatures reach a high of -3 °C. Ridge wind southwest 20 km/h gusting to 65 km/h. Freezing level 700 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Watch for changing conditions today, storm slabs may become increasingly reactive.
Dial back your terrain choices if you are seeing more than 30 cm of new snow.
Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
Be aware of the potential for surprisingly large avalanches due to deeply buried 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.

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.