When you're skiing or snowboarding on the mountain, like backcountry skiing or snowboarding you want to be really careful.
Avalanches can happen when you trigger something. It could be that you were skiing or snowboarding on a weak surface.
One of the warnings is when the temperature of the top layer of snow decreases. Another warning is when the layer closest to the ground maintains it's temperature causing a temperature difference between the upper layer and lower layers of the snow. Evaporation is another one to watch out for because evaporation begins to occur in the lower layers disrupting the 'stability' of the snow above. When the upper layers of snow lose grip and begins to slide it can trigger an avalanche.
One last warning for everyone to be safe is to always to check the temperature, because when you're out on the mountain 30-50 degrees then it isn't safe to be skiing or snowboarding. Why? Less than 30 degrees are exposed to steeper terrains up in the mountain which can lead to an avalanche.