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Avalanche Forecast

Archived

Mar 5th, 2021–Mar 6th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Temperatures are expected to cool off throughout the day on Saturday, but there is still a lot of uncertainty surrounding the potential for persistent slab avalanches. Hedge your bets by sticking to conservative terrain.

Confidence

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

Weather Forecast

FRIDAY NIGHT - Mainly clear / moderate to strong southwest wind / alpine low temperature near 0 / freezing level 2500 m, dropping to 2000 m

SATURDAY - Mainly cloudy / moderate to strong southwest wind / alpine high temperature near -1 / freezing level 2000 m, dropping to 1500 m in the afternoon and to valley bottom overnight

SUNDAY - Mainly cloudy with isolated flurries, up to 5 cm / moderate to strong southwest wind / alpine high temperature near -5 / freezing level 1500 m, dropping to valley bottom overnight 

MONDAY - A mix of sun and cloud / light west wind / alpine high temperature near -5 / freezing level 1500 m, dropping to valley bottom overnight

Avalanche Summary

There is a lot of uncertainty with regard to how quickly temperatures will drop on Saturday, and how the persistent weak layers will respond to the cooling trend. Though often less of a concern than rapid warming, cooling in the wake of warm temperatures can also trigger a spike in avalanche activity. 

On Friday, at the time of publishing, there were a few reports of human-triggered wet loose avalanches up to size 1.5, explosive triggered cornices up to size 1.5, and one explosive triggered size 2 persistent slab avalanche on a northeast aspect.

On Thursday, there were several reports of natural loose wet avalanches up to size 1.5 as well as natural and human-triggered wind and wet slab avalanches up to size 2. There were also a few reports of size 2.5 natural persistent slab avalanches in the nearby Waterton National Park region.

On Wednesday there were several reports of natural size 1 wet loose avalanches on solar aspects in the afternoon.

Snowpack Summary

Warm temperatures and sunshine have made the snow surface moist in most areas. Dry snow may still be found on north aspects. The moist snow will change into a crust when temperatures finally dip back below zero. Wind slabs are likely still present on northerly aspects in the alpine and at treeline.

Up to 50 cm of snow sits above a variety of old interfaces that formed in mid-February. There is 60-100 cm sitting on a persistent weak layer that was buried in late January. These interfaces are mostly made up of sugary facets, hard wind pressed snow, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. Recent test results indicate that the late January persistent weak layer is potentially still quite reactive.

Terrain and Travel

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

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.