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Avalanche Forecast

Archived

Mar 17th, 2023–Mar 18th, 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 avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

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

Storm slabs formed earlier in the week may continue to be reactive to human triggers at upper elevations; especially on sunny aspects.

Northerly aspects at upper elevations will offer the best riding conditions.

Confidence

Moderate

Avalanche Summary

Numerous natural very large (up to size 3) storm and wind slabs were reported on primarily sunny aspects at treeline and above on Thursday. These avalanches were triggered by a mix of solar radiation or cornice failures.

Additionally, numerous rider triggered storm and wind slabs up to size 2 were reported on primarily sunny aspects in the alpine where the recent snow is sitting on a crust down 30-40 cm.

Snowpack Summary

Expect to find sun crust on the surface of steep, sunny aspects.

Strong solar radiation has settled the 30-50 cm of recent snow into a storm slab which has been especially reactive to human triggers on sunny aspects where it overlies a crust.

Strong southwest wind during the storm earlier in the week have added to slab formation on lee aspects at treeline and above.

The recent snow is sitting on a variety of surfaces. These include sun crust on sunny aspects and surface hoar (3-10 mm) on some shady and sheltered slopes.

The mid-snowpack is generally strong but the lower snowpack is a different story.

The November facets are still prominent at the base of the snowpack. They are showing signs of improving but this layer remains a significant concern in rocky, shallow, or thin to thick snowpack areas at treeline and above.

Weather Summary

Friday Night

Clear skies / 10 km/h south ridgetop wind / Temperature at treeline around -9 C / Freezing level valley bottom

Saturday

Mix of sun and cloud / 10 km/h south ridgetop wind / Temperature at treeline around -3 C / Freezing level 1600 m

Sunday

Mostly sunny / 20 km/h southeast ridgetop wind / Temperature at treeline around -2 C / Freezing level 1800 m

Monday

Cloudy with isolated flurries; 0-3 cm / 20 km/h southeast ridgetop wind / Temperature at treeline around -3 C / Freezing level 1600 m

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Avoid exposure to slopes that have cornices overhead.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • 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.

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.