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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 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

North Rockies, Kakwa, McGregor, Pine Pass, Tumbler.

Forecast snow and wind Saturday night and into 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.

Snowpack Summary

Recent snowfall amounts have varied widely across the region with Pine Pass, Core Lodge riding area, and the southwest receiving the highest amounts of 20-30 cm.

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 gaining strength and consists of rounding facets and melt-freeze crusts that are starting to degrade. A spotty surface hoar layer buried around January 4th can still be found between 60 to 80 cm. Avalanche activity has not been reported on this layer recently but it is still showing up in snowpack tests.

Near the base of the snowpack, a persistent weak layer composed of large and weak facets formed in November is strengthening slowly. This layer is most likely to be triggered in thin, rocky alpine and upper treeline terrain.

Weather Summary

Saturday night

Snow; 10-25 cm / Strong west ridgetop wind / Low -8 °C / Freezing level valley bottom.

Sunday

Snow; 10-25 cm / Strong west ridgetop wind / High -1 °C / Freezing level 1200 m.

Monday

Mix of sun and cloud / Light northwest ridgetop wind / High of -5 °C / Freezing level valley bottom.

Tuesday

Mostly sunny / Moderate northeast ridgetop wind / High of -18 °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.
  • Minimize exposure during periods of heavy loading from new snow and wind.
  • 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.

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.