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Avalanche Forecast

Archived

Mar 7th, 2021–Mar 8th, 2021

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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Lizard-Flathead.

Buried weak layers remain possible to be triggered by riders, where they exist. Cornices and sun-exposed slopes will deteriorate during the heat of the day, potentially increasing the likelihood of avalanche activity.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SUNDAY NIGHT: Cloudy with light snowfall then clearing, accumulation 2 to 5 cm, 30 km/h southwest wind, alpine temperature -8 C.

MONDAY: Clear skies, 10 km/h northeast wind, alpine temperature -6 C, freezing level rising to 1500 m.

TUESDAY: Mix of sun and cloud, 20 km/h southwest wind, alpine temperature -6 C.

WEDNESDAY: Mix of sun and cloud with afternoon snowfall, accumulation 2 to 5 cm, 20 km/h west wind, alpine temperature -8 C.

Avalanche Summary

No avalanches were observed on Saturday or Sunday, besides some small loose dry out of steep alpine terrain. The most recent avalanche activity was observed on Friday, where wet loose avalanches, cornices, and persistent slab avalanches were triggered by riders and explosives.

Snowpack Summary

Previous warm air temperature followed by a re-freeze created a crust on the snow surface in many areas, which is covered by a dusting of fresh snow. Dry snow may still be found on north aspects at upper elevations. Wind slabs are likely still present on northerly aspects in the alpine and at treeline 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 faceted grains, hard wind pressed snow, feathery surface hoar in wind-sheltered locations, and a melt-freeze crust on steep solar aspects. Periodic avalanches continue to be triggered on these layers. Check out this MIN for photos of the positioning of the layers in the snowpack.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.