Most avalanches occur on slopes between 30-45° with the highest chance of a slide between 35-40°; prime black diamond terrain. Sluffs usually occur on slopes with pitch great than 50-60°. Slope meters are easy to read and cheap to purchase. Open terrain and especially convex surfaces are areas to use the most caution. Avalanches rarely occur on ridges or slopes with dense tree cover. Shaded and sunny terrain can also have very different potential for an avalanche.
Recent Snow Fall:
Although we all love to hit fresh powder, this can be a dangerous time for avalanches as most are triggered 24 hours after a storm. This occurs because new snow creates added stress on older, weaker layers causing them to become unstable and create a sliding plane for a slab. Sluffs can also occur when the new snow forms a poor bond with the top layer.
Cornices and pillows (resembling the name) are densely packed concentrations of snow that are formed from the wind. Due to their natural heavy weight and large surface area, they can easily weaken an underlying layer of snow and release forming an avalanche. This release can be triggered by its own weight or that of a skier.
Rapid Temperature Changes:
A rapid change in temperature also causes hazardous situations. As this occurs the bond between snow layers can weaken significantly. At higher temperatures, the top surface can also melt and become heavy while water filtrates to lower layers further weakening bonds and creating slippery surfaces between layers. Wet snow balls running down a hill or being able to squeeze water from a snow ball are great indicators of this condition.
When a large mass of snow collaspes by a few inches due to a small pocket of air beneath the surface, this is major signal of weak snowpack. We all know that whoooomph sound followed by the crackling of snow. Another sign are snow cracks propagating from your ski tips when entering a slope. Both of these are very unsafe conditions and should be avoided totally by turning around immediately.
Natural Avalanche Activity:
When approaching the slope you intend to ski, it is important to look for natural avalanche activity. This is one of the best indictors of unstable snow conditions and it is wisest to avoid these areas.