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Avalanche Forecast

Archived

Apr 12th, 2021–Apr 14th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

North Rockies.

A prolonged warming trend will increase the likelihood of avalanche activity. Danger rating is for peak daytime warming. Check out this blog for further information on the influence of warming and how to manage it.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

MONDAY NIGHT: Clear skies, 10 km/h southwest wind, alpine temperature -4 C, freezing level near valley bottom.

TUESDAY: Clear skies, 10 to 20 km/h southwest wind, alpine temperature -1 C, freezing level rising to 1900 m.

WEDNESDAY: Clear skies, 10 km/h northwest wind, alpine temperature 3 C, freezing level near valley-bottom in the morning and rising to 2700 m.

THURSDAY: Clear skies, 20 km/h east wind, alpine temperature 5 C, freezing level 3000 m.

Avalanche Summary

A few small to large loose wet and wind slab avalanches were observed in the region on Sunday on sun-exposed slopes. A few large avalanches were also observed on north aspects out of alpine terrain in the south of the region.

Looking forward, avalanche activity is expected to spike during periods of daytime warming and quiet down as the night cools the region.

Snowpack Summary

Warm air and sunny skies are moistening the snow surface, at least up to around 1900 m and to the mountain tops on sun-exposed slopes during daytime warming, with a hard crust expected overnight and early-morning. On north aspects above 1900 m, 20 to 40 cm of recent dry snow likely prevails, which may have old wind slabs. Cornices are very large along many ridgelines.

The warming trend has the potential of reactivating deeper weak layers, including a layer from mid-February as well as basal layers in shallow, rocky terrain along the eastern slopes of the Rockies.

Terrain and Travel

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.

Problems

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.