Cloud and Precipitation Characteristics Aloft during Winter Precipitation Type Transitions at the Surface

During near-0°C winter storms, various precipitation types, such as freezing rain and ice pellets, form under similar atmospheric conditions. Thus, accurately forecasting winter precipitation types and their transitions is challenging. The characteristics of particles aloft play a key role in determining the exact surface precipitation types. The goal of this study is to characterize the cloud and precipitation particles aloft during winter precipitation-type transition. To do so, the data collected during the 2022 Winter Precipitation Type Research Multiscale Experiment (WINTRE-MIX) field campaign, held in the Saint-Lawrence Valley River, were used. During this campaign, 12 precipitation-type transitions were identified. Numerical simulations using the Global Environmental Multiscale (GEM) model coupled with the latest version of the Predicted Particle Properties microphysics scheme were conducted. First, the cloud and precipitation particles simulated aloft will be compared with in situ measurements aloft and surface observations. Then, the cloud and precipitation characteristics aloft before and after precipitation-type transitions will be investigated. These include the changes in the particle sizes and the degree of riming because they impact the fall speed and the degree of melting and, in turn, the type of precipitation reaching the surface. Preliminary results indicate an increase in rime mass aloft during a transition from freezing rain to ice pellets, suggesting that denser precipitation particles aloft, probably only melted partially before reaching the subfreezing layer. This study highlights the necessity for detailed consideration of conditions aloft to accurately forecast precipitation-type transitions in near 0°C winter storms.