Avalanche Forecast

Archived

May 2nd, 2023–May 3rd, 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.

Newly formed slabs could be touchy to human traffic. Be aware of the variety of avalanche problems that you could come across during spring weather.

Confidence

Low

Avalanche Summary

Riders could trigger newly formed storm or wind slab avalanches within the snow that accumulated on Tuesday with strong southerly wind.

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

New storm and wind slabs likely accumulated at alpine elevations on Tuesday, with the most snow near White Pass and Haines Pass and less as you move east. The snow accumulated on a hard melt-freeze crust.

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

Spring-like weather prevails for the coming days, with overnight cooling and daytime freezing levels rising to around 1000 m to 1500 m. A mix of sun and cloud is expected, with isolated flurries.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Carefully evaluate steep lines for wind slabs.
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.
Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.