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Avalanche Forecast

Archived

Feb 18th, 2023–Feb 19th, 2023

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 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.

Regions

North Columbia, South Columbia, Esplanade, Jordan, North Selkirk, Shuswap, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, North Okanagan, Retallack, Valhalla, Whatshan.

Forecast snow and wind on Sunday will build reactive storm slabs. Large, natural avalanches may occur at upper elevations and human-triggered avalanches are expected at all elevations.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Confidence

Moderate

Avalanche Summary

Forecast snow and wind on Sunday will build reactive storm slabs. Large, natural avalanches may occur at upper elevations and human-triggered avalanches are expected at all elevations.

On Friday, a naturally triggered size 2 persistent slab that likely failed on a crust down around 100 cm was reported on a west aspect below treeline near Joss mountain.

Additionally, natural and human triggered wind slabs were reported up to size 2.5

Snowpack Summary

5-15 cm of new snow on Friday night brings recent snowfall totals to 40-60 cm. The recent snow is settling into storm slabs that will be most reactive where either wind has stiffened the snow or they overlie a layer of recently buried surface hoar.

Forecast snow and wind on Sunday will build reactive storm slabs. Large, natural avalanches may occur at upper elevations and human-triggered avalanches will be likely at all elevations.

The mid-pack is generally well consolidated with a few operations reporting continued snowpack results on a spotty surface hoar layer down roughly 80 cm. Reports of large avalanches involving various layers of surface hoar/crusts and facets within the mid-pack depth are sporadic but are a reminder of the complicated snowpack across this region.

In the lower snowpack, a layer of large and weak facets from November near the base of the snowpack is slowly gaining strength but there continues to be low confidence in this layer. Large destructive avalanches are the result of this layer being triggered.

Weather Summary

Saturday night

Snow; 5 to 10 cm / Moderate west ridgetop wind / Low -10 °C / Freezing level valley bottom.

Sunday

Snow; 10-25 cm; another 10-20 cm Sunday night / Strong west ridgetop wind / High -2 °C / Freezing level 1000 m.

Monday

Cloudy with flurries; 3-5 cm / Light northwest ridgetop wind / High of -3 °C / Freezing level 800 m.

Tuesday

Cloudy with flurries; 5-10 cm / Light southeast ridgetop wind / High of -10 °C / Freezing level valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Avoid all avalanche terrain during periods of heavy snowfall.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Use small low consequence slopes to test the bond of the new snow.

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.

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.