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Avalanche Forecast

Archived

Apr 29th, 2023–Apr 30th, 2023

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

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

Be aware of the variety of avalanche problems that you could come across during spring weather.

Confidence

Moderate

Avalanche Summary

A rider triggered a storm slab on steep northeast aspect at 1900 m on Friday. Numerous natural wet loose and storm slabs were also observed in the region.

We could see a variety of avalanche problems resurface during spring weather. Milder weather and periods of sun or rain promote wet loose or slab avalanches. Snow near the mountain tops could form wind slabs in lee terrain features. Cornices are large and looming and are more prone to fail which each day of relatively mild weather. The likelihood of triggering buried weak layers also increases in the spring, as the snowpack progressively warms up.

Snowpack Summary

Warm air to the mountain tops moistened the snow surface on Saturday, which likely froze into a melt-freeze crust. Rain at lower elevations could re-moisten the snow surface. Lingering wind slabs may be found in steep, lee terrain features from recent snow and strong southerly wind.

A weak layer of facets and potentially a melt-freeze crust from early January is between 100 and 200 cm deep in most areas.

Weak faceted grains may exist near the base of the snowpack, particularly in shallower snowpack areas.

Cornices are very large and looming along alpine ridges.

Weather Summary

Sunday to Tuesday sees mostly cloudy skies with some sunny breaks, a freezing level around 1300 m to 1500 m, light rain at lower elevations and snow up high, and moderate to strong south to southwest wind.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid avalanche terrain during periods of heavy rain.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Even brief periods of direct sun could produce natural avalanches.
  • Carefully evaluate steep lines for wind slabs.

Problems

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.

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.