Numerous changes to the winter output fields were made in the January 2023 implementation of NBMv4.1. Most notably are the increase in the number of model inputs (18 to 100) and the inclusion of the direct model output dominant precipitation type (p-type). The latter modifications now define the p-type product as non-conditional as opposed to conditional, meaning p-type forecasts are only produced where models produce precipitation. Expert weighting of the individual model p-types is used to generate a probability of each p-type occurring and identifying a categorical p-type. A brief overview of these v4.1 improvements will be presented.
While NBMv4.1 Winter products demonstrate an overall noteworthy improvement over the previous version, some challenges remain: (1) removing the inconsistencies noted between the expected deterministic and probabilistic NBM winter accumulations; (2) improving the downscaled quantitative precipitation forecast for lower resolution ensemble members used in calculating snow amounts. (3) improving the accuracy of snowfall accumulation products in marginal thermodynamic environments.

