15.8 Dynamics of heavy precipitation during Snow-V10

Friday, 3 September 2010: 9:45 AM
Alpine Ballroom A (Resort at Squaw Creek)
Mindy Brugman, Environment Canada, Vancouver, BC, Canada; and J. A. Milbrandt, G. A. Isaac, P. Joe, R. M. Rasmussen, F. S. Boudala, I. Gultepe, R. Mo, E. F. Campos, R. E. Stewart, T. Smith, C. Doyle, P. A. Bergeron, and J. Hay

Heavy winter precipitation associated with strong warm advection shows a flow reversal and precipitation enhancement that is separate from the lowest level diabatic (latent heat) effects. During the Vancouver 2010 Olympics, the Whistler Radar flow reversal pattern (see Figure 1) was not only repeatable, but also appeared to develop during the heaviest winter precipitation events. Multiple “bright bands” were also associated with the flow reversals and a bright radar reflection typically observed immediately above a flow reversal. The dynamics of heavy precipitation appears to involve these flow reversal processes. There is reason to believe that during strongly sheared flows with mixed phase (rain and snow) precipitation we may expect to observe these double-layered flow reversal patterns, and this is a first attempt to document this complex pattern. The cloud physics indicated by precipitation type and intensity are used to probe these complex radar patterns observed. The possible roles of nucleation in a turbulent shear layer, double diabatic layers due to humidity layering, and gravity waves are compared. The Snow-V10 data set obtained from 2009 to 2010 forms the basis of this project, and focus is placed on the Vancouver 2010 Olympic and Paralympics winter games period. Several cases of heavy precipitation when this feature appeared will be identified and evaluated. This project will include analysis of radar, satellite, surface, model, and snow level data and will focus on precipitation type results to-date. This paper includes an examination of recent wintertime heavy precipitation events over the BC south coastal mountains to better understand how frequently the heavy precipitation events were accompanied by similar flow reversals. Focus in this paper is placed on the relationship of observed dynamics to precipitation type– including rain, freezing rain, sleet, graupel and snow character such as degree of riming or aggregation. The aim of this project is to improve our knowledge of mountain meteorological processes through understanding the dynamics of heavy precipitation events during Snow-V10. Figure 1. Example of double flow reversal from Whistler VVO doppler radar taken Feb 14, 2010 00:10UTC (Valentines eve) scanned along an azimuth of 187 degrees. Cool colors (blue-purple-green) indicate southerly motion towards the VVO radar, and warm colors (red-pink-orange) indicate motion away from the radar (or northerly) on this cross section. This radar is located just south of the entrance to Callaghan Valley and is beside the Whistler dump site. Reference Snow-V10 Project data set.

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