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Avalanche Forecast

Archived

Feb 9th, 2022–Feb 10th, 2022

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

Purcells.

VKeep an eye on daytime warming and solar input. There is uncertainty in freezing levels and how the snowpack will react. Avoid overhead hazard.

Confidence

Low - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

Wednesday night: possibility of light rain. Freezing levels staying around 2200m. Moderate to strong west winds in the alpine.

Thursday: Mainly sunny with light to moderate northwest wind. Freezing levels in the morning around 2500m and gradually falling throughout the day.

Friday: sunny with Freezing levels around 1600m . Light northwest winds.

Saturday: Mostly sunny with a high of -2 at 1700m. Light northwest winds.

Avalanche Summary

On Tuesday several small cornice falls were observed triggering slab avalanches up to size 2 in lee and cross loaded features at treeline and above. A skier triggered a size 1.5 slab avalanche on a steep treeline feature on a south aspect, this avalanche ran on the late January layer.

On Sunday, several natural wind slabs and loose avalanches were reported. A skier remotely triggered a size 1.5 wind slab from 3 m away on an east aspect at 2500 m. Explosives triggered a number of slab avalanches size 1.5-2.5 in the deeper west part of the region where the slab thickness was typically 30-50 cm and up to 120 cm in wind loaded terrain. 

This MIN post from the Dogtooth shows the type of open slopes where the buried surface hoar may be reactive at lower elevations.

Snowpack Summary

With high freezing levels and sunny skies moist snow will likely be observed on all aspects at and below treeline as well as south facing slopes in the alpine.

Previous strong wind from the southwest through northwest have formed wind slabs in exposed terrain at higher elevations. 

The January 30 interface is now typically down 20-50cm and consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine, surface hoar in sheltered areas at and below treeline, and small facets in some areas.

Several old surface hoar layers are now buried in the upper snowpack 40-90cm deep.  

The early December crust/facet layer of concern sits around 80 cm deep in the eastern Purcells and shallow terrain, and up to 150 cm in the west. This layer produced numerous large avalanches in January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Avoid exposure to slopes that have cornices overhead.
  • Be careful as you transition into wind affected terrain.

Problems

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.