An Examination of Winter Precipitation at Cypress Mountain, BC, during SNOW-V10

Cypress Mountain, located just north of Vancouver, is a typical coastal barrier for moisture-laden onshore airflow and, therefore, is subjected to large amounts of precipitation. The athletic events at this site during the 2010 Vancouver Olympic Winter Games (snowboarding and freestyle skiing) were plagued by postponements due to the lack of snow. Substantial amounts of rain occurred instead. Unprecedented data on precipitating systems affecting this mountain were obtained between January and April 2010 as part of the SNOW-V10 (Science and Nowcasting Olympic Weather for Vancouver 2010) field campaign. This included information collected from a Micro Rain Radar (MRR), Precipitation Occurrence Sensor System (POSS), and enhanced surface weather stations, as well as from operational radars and satellite data. Some precipitation events lasted upwards of 24 h, although moderate to heavy precipitation rates lasted to a maximum of approximately 6 h. Vertical radar profiles revealed the common occurrence of precipitation aloft and an increase in intensity towards the surface. Inferred heights of the melting layer just upwind of the barrier were compared with the heights observed on the mountain; the height of associated precipitation on the barrier was sometimes different by as much as a few hundred metres. Utilizing these data, the study's objective is to quantify the means through which precipitation is produced on this barrier paying particular attention to the transition regions between rain and snow. This study has important implications for assessing the exact means through which precipitation is produced on the coastal mountain range, especially during El Niño conditions, and for improving nowcasting and forecasting.