Most Tree Well/ SIS accidents have happened during or just after big snow storms or storm cycles. In general terms, the more fresh snow the higher the risk. As of 2011 research, an average of four Tree Well / SIS accidents happen each season in the United States.

Most all Tree Well/ SIS accidents happen in ungroomed terrain. A groomed run is a ski or snowboard run that has been driven on by a snow machine to compact and consolidate the snow.

• Most Tree Well/ SIS accidents happen where there are combinations of deep powder and trees and where lots of powder skiers and snowboarders are seeking powder snow.
• Lots of deep loose snow makes for the best powder skiing conditions. Unfortunately these conditions also significantly increase the chance of a Tree Well/ SIS accident.
• 70% of all Tree Well/ SIS accidents involve tree wells. Deep snow Tree Well/ SIS accidents occur in areas of deep snow, deep snow pockets or terrain that concentrates deep snow such as steep drops, and creek beds.

The risk of a Tree Well / SIS accident is greatly reduced just by staying on groomed runs.

Volunteer Skier being Rescued by Ski Patrol During Tree Well Experiment.

This small tree in ungroomed area was the site of a fatal tree well accident.