Avalanche Forecast

Archived

May 5th, 2023–May 6th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

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

Low

Avalanche Summary

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 storm slabs or 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

Small storm or wind slabs may linger in the high alpine, particularly where they sit on a hard melt-freeze crust. At treeline and lower alpine elevations, a hard melt-freeze crust is likely found on the snow surface. The snow surface will moisten during daytime warming, particularly on sun-exposed slopes and at lower elevations.

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

The freezing level will rise to 1400 m during the heat of the day and drop to below valley bottom overnight until Monday. Saturday and Sunday are a mix of sun and cloud and Monday is mostly cloudy with light flurries.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Avoid steep slopes when air temperatures are warm, it is raining, or solar radiation is strong.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
Carefully evaluate steep lines for wind slabs.
Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.

Problems

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.

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.