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Avalanche Forecast

Archived

Feb 2nd, 2021–Feb 3rd, 2021

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 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 Columbia.

Human triggering of large storm slabs remains likely on Wednesday. Storm slabs may be surprisingly large and easy to trigger due to the presence of buried weak layers of surface hoar.

Confidence

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

Weather Forecast

  

TUESDAY NIGHT: Flurries; 3-5 cm. / Light, northwest ridgetop wind / alpine low temperature -10 / Freezing level valley bottom.

WEDNESDAY: Mix of sun and cloud / Light, west ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

THURSDAY: Flurries; 3-5 cm. / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.

FRIDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

Avalanche Summary

On Monday, several skier triggered storm slab avalanches up to size 2 on surface hoar were reported in the gorge area and natural avalanches up to size 3.5 were reported just east of the region in glacier national park.

A widespread natural cycle and numerous skier triggered storm slab avalanches up size 2 were reported on all aspects in the Gorge area west of Revelstoke on Sunday. These storm slab avalanches were running on a weak layer of surface hoar that was buried by the recent storm. See one of numerous MIN reports Here.

Touchy storm slabs are sitting on a very weak layer of surface hoar which is likely to be reactive to human triggers. Avalanches may be larger than expected due to the presence of this weak layer.

Snowpack Summary

20-30 cm of new snow brings recent snow totals to 60-90 cm. Rising freezing levels throughout the storm and moderate, southerly winds have caused rapid slab formation. These touchy storm slabs are sitting on multiple weak layers of surface hoar which have potential to surprise backcountry users by how easily they may be triggered and how wide the slabs propagate across slopes. The first sits below the recent snow and the second is around 60-90 cm. down.

Observers continue to find a third layer of surface hoar from earlier in January down 90-120 cm. in sheltered, open areas near treeline. New snow loads have the potential to awaken these deeper persistent weak layers.

The lower snowpack is generally well settled and strong. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Be careful as you transition into wind affected terrain.

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.