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Avalanche Forecast

Archived

Nov 28th, 2020–Nov 29th, 2020

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
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, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

 15-25 cm. of recent storm snow and strong southerly winds have created wind slabs at treeline and above. These wind slabs may be surprisingly reactive in areas where they are sitting on a layer of small surface hoar.  

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

 SATURDAY NIGHT: Few clouds / Moderate, south wind / alpine low temperature -12 / Freezing level valley bottom.

 SUNDAY: Mix of sun and cloud / Moderate, south wind / alpine high temperature -5 / Freezing level 1000 m.

 MONDAY: Snow, 5-10 cm / Strong, south wind / alpine high temperature -5 / Freezing level 1000 m.

TUESDAY: Mostly sunny / Light, northwest wind / alpine high temperature -6 / Freezing level valley bottom.

Avalanche Summary

There have been very few reports of avalanches in the region, however, observations are very limited at this time. Several recent MIN reports from neighboring Glacier National Park have reported human triggered avalanches on small surface hoar below the recent storm snow.

If you get out into the mountains, please consider sharing your observations on the Mountain Information Network!

Snowpack Summary

 15-25 cm of recent storm snow and strong southerly winds have created wind slabs at treeline and above. These wind slabs may be surprisingly reactive in areas where they are sitting on a layer of small surface hoar. This layer has been described as “spotty” and may only be found in specific areas. A crust from early November exists down approximately 90-130 cm. This crust has been observed to have weak, sugary facets above and below it. Recent tests on this layer indicate that it may be bonding poorly, and has the potential to be triggered by humans. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid lee and cross-loaded terrain.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.