Warmer weather, whether seasonal or global, plays havoc with snow layers, creating 'variable snow pack'. Conditions, and the snowpack, can change throughout the day.
If, in warmer weather, you ski onto a slope that others are skiing or that has clear tracks, without doing your own risk assessment, first, it’s naive to assume that 'if they're skiing that slope, I can too' and second, it’s dangerous. At least be aware of the seasonal risks and whether or not you’re competent to assess the situation. Skiing or snowboarding with a trained local guide in springtime terrain is an excellent choice.
Ski slopes with tracks on them can make it safer in some respects. Studies show that boot packing a slope has a much more stabilizing effect than skiing the slope. Never assume a slope safe to ski because it is tracked-out or because it's not closed off. There are plenty of examples of tracked-out slopes that morphed into big avalanches.
Another misconception about avalanches is that they don't occur (as much) in trees. Ah, they Do!
Wet Slab Avalanches
These occur when a slab of snow slides on a wet, lubricated layer of snow beneath it. Unlike dry slab avalanches, which occur on dry snow, wet slab avalanches are triggered by melting snow and water saturation within the snowpack. Look for warming, rotting spring snow, at the transition from rocks to deeper snow. This is a classic trigger point in any condition, and especially in warming conditions.
Factors that contribute to wet slab avalanches:
Wet Snow Layer: when the temperature rises, it causes the snowpack to melt and become saturated with water, and a wet slab avalanche typically occurs. Or, water percolates through the snowpack, creating a lubricated layer (often referred to as a "slick" layer) between the slab of snow above and the underlying snow layers.
Slab Release: the weight of the wet snow slab becomes too heavy for the lubricated layer to support, causing the slab to release and slide downhill. These avalanches can vary in size and speed depending on the volume of the slab, the angle of the slope, and terrain features.
Conditions Favoring Wet Slab Avalanches: warm temperatures and direct sunlight accelerates snowmelt and increases the risk of a wet slab avalanche. Rainfall can quickly saturate the snowpack, weakening the snow layers and increasing the likelihood of slab releases. Alternating freezing and thawing can create a crust on the snow surface, trapping water beneath and contributing to wet slab formation. Weak or faceted snow layers within the snowpack can contribute to instability, especially when subject to melting and water infiltration.
Terrain and Slope Angle: wet slab avalanches are more common on steep slopes with a slope angle between 30 to 45 degrees. Terrain features like convexities, gullies, and unsupported slopes can increase the risk of wet slab avalanches because of the accumulation of water and stress on the snowpack.
Impact: these avalanches can be extremely destructive as they carry huge volumes of snow, ice, and debris downhill. They pose a significant risk to backcountry travelers, skiers, snowboarders, and anyone in or near avalanche terrain. The wet, heavy nature of the avalanche debris can make it difficult for avalanche rescue teams to conduct search and rescue operations.
Mitigate the risk: stay informed about current snow, weather, and avalanche conditions, and avoid traveling in or below avalanche terrain during periods of warm temperatures, rainfall, or rapid snowmelt. Using avalanche safety equipment, such as beacons, probes, and shovels, and having proper training in avalanche safety and rescue techniques is crucial when venturing into avalanche territory.
Further Reading: one of the best sources for information is the publication called ‘Snowy Torrents: Avalanche Accidents in the United States’ (published by the American Avalanche Association).
https://missoulaavalanche.org/2023/04/assessing-conditions-without-an-avalanche-forecast
Avalanche Courses:
https://www.bakermountainguides.com/how-much-does-avalanche-course-cost/
