Avalanche Forecast

Archived

Apr 28th, 2023–Apr 29th, 2023

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.

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.

A high freezing level will destabilize the snowpack, potentially triggering numerous different avalanche problems. Check out the latest Forecasters' Blog for more information.

Confidence

Moderate

Avalanche Summary

We haven't received any recent avalanche observations.

We expect a strong uptick of avalanches on Saturday as the freezing level is above mountain tops. Expect to see loose wet or slab avalanches, cornice falls, lingering wind or storm slabs, and potentially large avalanches releasing on buried weak layers.

Snowpack Summary

Warm air to the mountain tops will moisten the snow surface. 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. They could release as wet slab avalanches as the upper snowpack moistens.

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

Saturday will see a freezing level to 2300 m with periods of rain. Light rain or snow is expected for Sunday and Monday with a freezing level around 1500 m and 1200 m, respectively. The wind is expected to remain moderate to strong from the south to southwest.

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.

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.

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.