FTS (Fog To Snow) Conversion Process During the SNOW-V10 Project

Abstract

The objective of this work is to understand how winter fog which occurred on Whistler Mountain on 3–4 March 2010 developed into a snow event by the means of the FTS (Fog To Snow) process. This event was documented using data collected during the Science of Nowcasting Winter Weather for Vancouver 2010 (SNOW-V10) project that was supported by the Fog Remote Sensing and Modelling (FRAM) project. The FTS resulted in a snow event at about 1,850 m altitude where the RND (Roundhouse) meteorological station was located. For both days, there was no large scale system that affected local fog formation and its development into snow. Patchy fog occurred in the early hours of both days and was based below 1,500 m. Clear skies at night likely resulted in cooling, the valley temperature (T) was about −1°C in the early morning, and snow was on the ground. Winds were relatively calm (<1 m s−1). At the RND site, T was about −3°C. Weather at RND was clear and sunny till noon. When fog moved over the mountain peak/near RND, light snow started and lasted for about 4–5 h and was not detected by precipitation sensors except the Ground Cloud Imaging Probe (GCIP) and Laser Precipitation Sensor (LPM). In this work, the FTS process is conceptually summarized. Because clear weather conditions over the high mountain tops can become hazardous with low visibilities and significant snow amounts (<1.0 mm h−1), such events are important and need to be predicted.