When cold, dry snow becomes wet for the first time, it almost always means wet sluffs (loose snow that fans outward as it descends).
Larger wet slab avalanches can happen when melt water percolates through a layered, winter snowpack for the first time especially after 3 days of strong melting combined with no refreeze at night.
Luckily, wet avalanches usually don't last forever because over time, days or weeks, of percolating melt water, all the layers in the snow disappear and the snow becomes homogenous and dense, turning into a stable summer-like snowpack. Typically, this cycle of instability maturing into stability occurs first on the south facing slopes in early spring, then progresses to the east and west facing slopes in mid spring and finally by late spring, the upper elevation north facing slopes go through a wet avalanche cycle.
Finally, glide avalanches occur regularly in spring as the entire snowpack slides slowly on the ground like a glacier until they suddenly release into a full-depth avalanche. These occur regularly on steep rock slabs and occasionally on steep grassy slopes. Notorious glide avalanche locations include places Stairs Gulch or the rock slabs in Broads Fork, which you should always avoid in spring. Avoid crossing under any slopes with telltale glide cracks in the snowpack. Remember they come down randomly, even at night.
The bottom line for wet avalanches:
Get out early and get home early. Get off of--and out from underneath--any slope approaching 35 degrees or steeper when the snow becomes wet enough to not support your weight. Warning signs may include:
- Roller balls (pinwheels) in new snow that is getting wet for the first time
- Natural or human triggered wet sluffs
- Small sluffs fanning out into larger slides, or running long distances
- Cornices breaking off
- Several days of strong melting combined with no refreeze at night
Any of these signs mean it's time to head home, or at least change to an aspect with cooler snow. Remember, even "smaller" slides can be dangerous in high-consequence terrain, such as above a terrain trap, trees, rocks, cliffs or a long, large avalanche path. Plan your trip to have a safe exit back to the car.
