The new probabilistic mountain weather forecast is being provided for the remainder of this season as a demonstration for our snow safety partners in Little Cottonwood Canyon and Provo Canyon to evaluate the utility of added probabilistic data and new forecast visualizations. The operational mountain weather forecast has long provided a simple probabilistic snowfall (and water content) forecast, while many other fields of the forecast like temperature, snow ratio, snow level, and wind provided deterministic forecast values.

The main goal of developing the new probabilistic mountain weather forecast is to better communicate the range of potential outcomes in the forecast, while also making timing and trend information more readily apparent with visualizations. This includes using more robust science and statistics behind each probabilistic field by leveraging the extensive amount of ensemble forecast information now available.

The snow and water amount forecasts are based on the Probabilistic Snowfall Forecasts with the human forecaster able to modify the probabilistic information as needed. The temperature, snow level, snow ratio, and lightning fields are based on the official NWS point forecast with the spread for each variable derived from the National Blend of Models (includes 100 ensemble members and a mix of high resolution and global models). Wind direction, speed, gusts, and uncertainty are based on in-house model blends. The human forecaster retains the ability to adjust the median or max value of each of these parameters.

The new probabilistic forecast is considered a beta / test product for the remainder of this season as we gather feedback and input that will inform how this product evolves in the future to meet the snow safety partners' needs. While the new probabilistic forecast will generally have the influence of a human forecaster, it should be treated as an experimental product and used with caution, while the legacy mountain weather forecast remains the official snow safety forecast.