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Avalanche Forecast

Archived

Apr 27th, 2023–Apr 28th, 2023

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

Regions

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

Travel cautiously and expect to find wind slabs in steep terrain. The possibility remains of triggering buried weak layers. For more information about the incoming warming, check out the latest Forecasters' Blog.

Confidence

Moderate

Avalanche Summary

We haven't received any recent avalanche observations. Going forward, we expect that riders could trigger wind slabs in steep terrain features and potentially storm slabs in steep wind-sheltered terrain.

The likelihood of triggering a buried weak layer will increase as the freezing level rises on the weekend. Wet loose avalanches are also possible during any period of sunny skies.

Avoiding cornice exposure is also a good idea, as they are very large and could fail naturally or under the weight of a human.

Snowpack Summary

Wind slabs may be found in steep, lee terrain features from recent snow and strong southerly wind. Storm slabs could prevail in wind-sheltered terrain. These slabs may sit on a hard melt-freeze crust found up to 1400 m and to mountain tops on sun-exposed slopes. The snow surface could moisten on sun-exposed slopes during periods of sunny skies.

A weak layer of facets and potentially a melt-freeze crust from early January is buried over 100 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

A mix of sun and cloud and isolated flurries is forecast for the coming days, with a freezing level around 1300 m for Friday, up to 2300 m for Saturday, and dropping back to 1500 m for Sunday. The wind is expected to remain moderate to strong from the south.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Cornice failure may trigger large avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Even brief periods of direct sun could produce natural avalanches.

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.

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.