Measurements of Hazardous Winter Precipitation in the St. Lawrence River Valley

Freezing rain and ice pellets are hazardous types of precipitation during the winter. Their differentiation is a challenge because both types of precipitation are produced in similar temperature structure, which is composed of a melting layer aloft and a refreezing layer below. The Saint Lawrence River Valley (SLRV) is the second region with the highest occurrence of freezing rain over North America. The wind channeling effects near the surface is partly responsible for the higher occurrence, producing favorable atmospheric conditions. This makes the SLRV a natural laboratory to improve our understanding of winter precipitation type formation. The goal is to measure, observe and document precipitation types associated with winter storms when the temperature is near 0°C. To do so, measurements from a MRR and optical disdrometer installed downtown Montreal as well as on a mobile weather station will be used. The automatic measurement will be combined with manual observations of precipitation types. Results from an ice pellets event that occurred in February 2019 over Montreal, Quebec, Canada, will be presented as well as other precipitation events document during the fall 2019. In particular, the vertical evolution of precipitation characteristics aloft and at the surface will be studied using the combination of instrumentation and high-resolution simulations. This work will contribute to better understand the precipitation processes aloft that are associated with ice pellets and freezing rain at the surface.