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Avalanche Forecast

Archived

Mar 4th, 2021–Mar 5th, 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 possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Avalanche danger could reach HIGH by the afternoon with sunshine and intense warming. Pay close attention to rising temperatures and the sun's intensity. Stick to simple, low-angle terrain and avoid overhead hazard, especially during the warmest part of the day.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

THURSDAY NIGHT - Mainly clear / moderate to strong southwest wind / alpine low temperature near 0 / freezing level 2300 m

FRIDAY - Sunny / moderate to strong southwest wind / alpine high temperature near 3 / freezing level 2400 m

SATURDAY - Mainly sunny in the morning and increasing cloud in the afternoon / moderate to strong southwest wind / alpine high temperature near 2 / freezing level 2400 m, dropping to valley bottom overnight 

SUNDAY - Mainly cloudy with flurries / moderate southwest wind / alpine high temperature near -6 / freezing level 1500 m 

Avalanche Summary

There were a few size 1 natural and human-triggered wet loose avalanches reported on solar aspects on Wednesday.

There were also reports of several size 2-2.5 natural wet loose avalanches in the neighbouring Waterton National Park region, and two size 2.5 natural persistent slab avalanches in the neighbouring Kananaskis Country region.

Sun and warm temperatures are our primary concern over the next few days. 

  • Large cornices may weaken and fail, triggering slabs on the slopes below. 
  • Loose-wet avalanches will likely be seen from solar aspects first and then possibly all aspects. 
  • The slab sitting above the persistent weak layers may stiffen and consolidate further, failing as a natural avalanche or becoming more sensitive to skier and rider triggers.  
  • Pockets of wind slab may be reactive on northeast-east aspects at upper elavtions. 

Snowpack Summary

Upper elevations are highly wind-affected and scouring down to rocks or crusts can be seen on west to southwest aspects. On leeward (northeast-east) slopes, stiff pockets of wind-slab have formed at treeline and in the alpine.

40-60 cm (in some places up to 100 cm) of snow sits above a persistent weak layer of facets that was buried in mid-February. Recent snowpack tests indicate that this layer is reactive and has the potential to propagate widely, causing large avalanches. 

There is another persistent weak layer that was buried at the end of January. This layer consists of surface hoar, facets, and/or a hard melt-freeze crust. recent MIN reports show that these layers remain easily triggered by people. 

Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack. 

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.

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.

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.