“No one ever steps in the same river twice.” -Heraclitus
You may have noticed that our forecast zone map has changed this year. After many meetings, rough drafts and inquiries with long time local experts, BTAC forecasters arrived at the current zone boundaries that have some advantages over the previous zones. Our work included maps of 30 years of monthly snowfall and temperature data, typical storm patterns, heat maps of public and forecaster observations since 2010, and other informal data such as known hot spots for recreation and trailhead locations.
Zones Lost
You’ll note that the forecast area was trimmed in regions such as the northern portion of the Togwotee zone which spanned into Yellowstone NP. We also trimmed off the southern tip of the Greys River/Southwest Trails zone. Both of these areas received only several observations in as many years. The eastern portion of the Gros Ventre area was also trimmed from our forecast area due to the large winter wildlife closures which exclude access and dearth of observations. Ultimately, our forecasting resources must be directed to areas of concentrated use combined with the most significant and dangerous avalanche terrain. These hard realities play a significant role in the decision to change forecast zone areas. We added an observation zone in the Big Holes to encourage the sharing of information through the BTAC observation platform. You can think of the Big Holes, the Gros Ventre and the Southern Wyoming Range as observation zones for now and aspirationally as future forecast zones.
Zones Added
Our research process led us to add the Snake River zone and restructure the Greys River/ SW Trails zone to include the Salt River, Wyoming, and part of the Gros Ventre range from Snow King to the Granite Creek Hot Springs. The Snake River area has seen a high concentration of avalanche fatalities and increased recreational use over the last decade. It also has a unique snow climate that can vary significantly from its neighbors. The Snakes lacked snow telemetry until this year when BTAC staff installed wind and snow stations near Mt Baird. Given the high number of annual observations, as well as the newly operational telemetry, we are confident that we can produce accurate daily avalanche forecasts for the Snake River Range.
Zone boundaries are tools that forecasters use to communicate risk, much like avalanche danger ratings. Danger ratings have been described as subjective boxes drawn on a scale which is a continuum of avalanche danger. There is no glaring and obvious line between two ratings but practitioners and recreationists need to work from a common set of assumptions in order to communicate. Similarly, the new zone boundaries create opportunities to recognize patterns and more clearly communicate the avalanche problems at play using the many graphical tools provided in the daily forecast.