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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

Lizard-Flathead.

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 1 / freezing level 2400 m

FRIDAY - Sunny / moderate to strong southwest wind / alpine high temperature near 4 / freezing level 2400 m

SATURDAY - Sunny in the morning and increasing cloud cover 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 -3 / freezing level 1500 m

Avalanche Summary

On Thursday, at the time of publishing, there were several reports of natural loose wet avalanches up to size 1.5 and natural 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.

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. 
  • Wet loose avalanches will likely be seen from solar aspects first and then possibly all aspects. 
  • The persistent slab sitting above 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 elevations. 

Snowpack Summary

Strong southwest to west wind has formed wind slabs on leeward slopes while freezing rain formed a widespread breakable crust on the surface below about 1800 m, and in spotty locations at upper elevations. 

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 surfaces, 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.