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Avalanche Forecast

Archived

Feb 21st, 2021–Feb 22nd, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

Regions

South Rockies.

 A storm will impact the region Sunday night into Monday, forming new slabs, destabilizing the snowpack, and increasing the likelihood of triggering buried weak layers. An avalanche cycle may occur at all elevation bands. Travel in avalanche terrain is not recommended. 

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

SUNDAY NIGHT: Cloudy with snowfall, accumulation 5 to 15 cm, 50 gusting to 100 km/h southwest wind, alpine temperature -6 C, freezing level 1300 m.

MONDAY: Cloudy with snowfall, accumulation 10 to 20 cm and local enhancements possible, 40 to 80 km/h southwest wind, alpine temperature -5 C, freezing level 1500 m.

TUESDAY: Cloudy with snowfall and afternoon clearing, accumulation 5 to 15 cm, 30 km/h west wind, alpine temperature -8 C.

WEDNESDAY: Clear skies, 20 km/h southwest wind, alpine temperature -10 C.

Avalanche Summary

Many small to large (size 1 to 2) wind slab avalanches have been triggered within the past week, such as this one.

Looking forward, new storm and wind slabs will form and likely be reactive to human traffic. Natural avalanche activity may occur, so best to stay well away from concerning avalanche terrain on Monday.

Snowpack Summary

New snow and strong wind will form new storm and wind slabs Sunday night into Monday above around 1500 m. Below, rain will soak the snow surface. The snow will overly hard wind affected surfaces in exposed terrain and sugary faceted grains in sheltered terrain. Ultimately, this new snow may not bond well to previous surfaces and increase the likelihood of avalanche activity.

Around 50 to 80 cm deep, a weak layer of surface hoar may be found in sheltered terrain or otherwise faceted grains and/or a hard melt-freeze crust.

Weak faceted grains and a decomposing melt-freeze crust are likely found near the base of the snowpack. There have not been recent avalanche observations on this layer, but steep and rocky slopes as well as shallow snowpack areas should be approached with caution.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Travel in alpine terrain is not recommended.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.