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Avalanche Forecast

Archived

Apr 8th, 2021–Apr 9th, 2021

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

Regions

Purcells.

Fresh snow amounts are variable across the region, and may have formed reactive wind slabs on many aspects due to changing wind directions. 

Keep in mind that even brief periods of sun can initiate natural avalanche activity in the new snow. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Unsettled weather continues with more snow, strong winds, and seasonally cool temperatures. More sun and fewer snowfall amounts than forecast below for the Dogtooth Range.

Friday: Cloudy with light snow 5-10 cm. Ridgetop wind moderate to strong from the southwest. Alpine temperatures near -9 and freezing levels 1300 m.

Friday Night: Snow amounts 5-10 cm with strong southwest winds at ridgetop.

Saturday: A mix of sun and cloud with convective flurries up to 10 cm. Ridgetop wind strong from the northwest. Alpine temperatures near -9 and freezing levels 1000 m. 

Sunday: A mix of sun and cloud with light ridgetop wind from the northwest. Alpine temperatures -9 and freezing levels 1500 m. 

Avalanche Summary

On Thursday, dry loose avalanches up to size 1 were reported from steep terrain features and a significant natural cornice failure triggered a persistent slab from the slope below size 3. This occurred on a high alpine steep east-facing slope. 

The weather pattern is spring-like which can bring intense periods of solar radiation and convective power flurries. Get after it early before daytime warming kicks in and solar radiation weakens the snowpack and cornices. Loose surface avalanches within the new snow may occur from steeper slopes and terrain features, especially if the sun comes out.

Stay well back from ridgetops that are corniced and avoid slopes with overhead cornice exposure especially under the current conditions where recent rapid growth and daytime warming has made them large and fragile. 

Snowpack Summary

5 cm to 10 cm of new snow fell across the region. Shifting wind directions from the southwest to northwest could form isolated pockets of wind slab on leeward slopes and behind terrain features. The new snow fell on a series of melt-freeze crusts exist on all aspects below 1900 m and solar aspects to mountain top. Sluffing in the new snow sliding on the crust may exist. North aspects in the alpine hold dry wintery and wind-affected snow. The mid-pack is generally strong and consolidated. 

A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and a small surface hoar and facets have been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers but isolated instances of large solar-triggered slab avalanches running on the crust have been observed. The early November crust is buried down 180-200 cm and has faceted crystals above and below it. This is currently dormant but something to keep in mind during the next big warm-up. 

Terrain and Travel

  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
  • Carefully evaluate bigger terrain features on an individual basis before committing to them.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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.