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Avalanche Forecast

Archived

Nov 27th, 2020–Nov 28th, 2020

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, 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.

Regions

North Columbia.

  

Recent snow and strong southwest winds have formed widespread storm slabs reactive to human triggers. Make conservative terrain choices as you gather information about the bond of the new snow.

Confidence

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

Weather Forecast

  

FRIDAY NIGHT: Snow; 5-10 cm / Moderate to strong, southwest wind / alpine low temperature -10 / Freezing level valley bottom.

 SATURDAY: Mix of sun and cloud / Light, west wind / alpine high temperature -5 / Freezing level 800 m.

 SUNDAY: Mix of sun and cloud / Moderate, south wind / alpine high temperature -6 / Freezing level 1000 m.

 MONDAY: Snow, 5-10 cm / Moderate, south wind / alpine high temperature -3 / Freezing level 1200 m.

Avalanche Summary

Storm slabs are expected to be reactive to human triggers on Saturday.

There have been very few reports of avalanches in the region, however observations are limited at this time. 

In the past week there have been a few size 2-3 avalanches reported on the early November crust in both the North Columbia and neighbouring Glacier National Park region.  

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

Snowpack Summary

Recent storm totals are expected to be around 15-25 cm by Saturday morning. The biggest snowfall amounts are expected to be in the northern half of the region. Storm slabs will likely be widespread in the region. 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

  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be careful to keep storm day fever from luring you out into bigger terrain features.

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.