Improta says weather, terrain and snowpack make up the three factors needed for an avalanche. Avalanches are difficult to predict, but sometimes the mountaineer is just in the wrong place at the wrong time, Improta said. Avalanches are most likely to happen after storms, prolonged temperature changes, abrupt temperature changes or high winds. They occur frequently in gullies that are drainages for the snowpack, and slopes with snowpack that has a weak base layer. During the winter, avalanches occur mostly on north and east slopes and in the summer on south slopes, Improta said.
Slabs are most dangerous and almost impossible to outrun.
They occur when a weak layer in the snowpack gives way. Loose snow avalanches move slower, yet can be just as deadly in spring when they carry heavy, wet snow, Improta said. Thompson said some avalanches ride on a cushion of air because of the compression. Since air has a low efficiency of friction, avalanches can accelerate to speeds around 80 mph. In the backcountry, using transceivers and digging snow pits to evaluate conditions are important precautions, but preparation is key, said Improta.