The chance of an avalanche releasing within a specified area and time period.
Likelihood of avalanches is the chance of an avalanche releasing within a specified area (typically a forecast region or elevation band within that region) and time period (typically the forecast period: today). The likelihood is a function of how sensitive avalanche conditions are and how widely distributed the instabilities are. Forecasters use a range of qualitative terms to express likelihood judgments independently of the scale of terrain. The likelihood matrix shows how each term is defined.
To further illustrate these definitions as they are used in forecast products, here’s what we would expect you to encounter if you wandered aimlessly and randomly throughout avalanche terrain all day, without any sense of avalanche awareness:
- Unlikely: Your odds of triggering an avalanche are very low but not impossible. Your day should go uneventfully without triggering or encountering an avalanche.
- Possible: There are a handful of problematic steep slopes where you could encounter an avalanche today. When avalanches are “possible”, you will return home without an avalanche encounter more often than triggering an avalanche, but both outcomes can be expected from time to time.
- Likely: The odds are favorable that you will encounter or trigger an avalanche today. You should trigger several of the steep slopes that you cross and/or some terrain will avalanche naturally.
- Very Likely: Most of the steep terrain that you travel on will avalanche, and you’ll encounter numerous natural avalanches.
- Almost Certain: You will trigger an avalanche on almost all of the steep terrain that you cross–if it hasn’t already released naturally–throughout the day. If you look around, you’ll witness a widespread avalanche cycle.