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

Regions

Sea To Sky.

Although the storm has subsided, human triggered avalanches remain likely, especially in wind loaded areas. 

Keep in mind that a persistent weak layer is now buried up to 100 cm. Avalanches on this layer will become harder to predict, so a conservative approach is important.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

TUESDAY NIGHT - Mainly cloudy with a few flurries / light southwest wind, switching to light north wind / alpine low temperature near -10 

WEDNESDAY - Sunny with cloudy periods / light north wind / alpine high temperature near -9

THURSDAY - Mainly cloudy with a few flurries, / moderate west wind / alpine high temperature near -7 

FRIDAY - A mix of sun and cloud / light to moderate west wind / alpine high temperature near -5

Avalanche Summary

Avalanches are expected to remain easy to trigger on Tuesday in many areas, especially in wind loaded terrain at higher elevations.

There have been reports of size 1-2 natural, human and explosives triggered avalanches every day since Saturday. Many of these avalanches have failed on the recently buried persistent weak layer.

Snowpack Summary

50-100 cm of recent fresh snow sits on a persistent weak layer that consists of facets at upper elevations, surface hoar in sheltered areas, a melt-freeze crust below 1900 m, and a sun crust on south-facing slopes. There could be more than 100 cm on this layer in wind loaded areas.

A crust from early December may be found around 200+ cm deep in the snowpack. In shallow rocky areas, it may still be possible to trigger this layer. In deeper snowpack areas, it appears to be unreactive.

Terrain and Travel

  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.