Pure Appl. Geophys. 171 (2014), 157–183 Ó 2012 Her Majesty the Queen in Right of Canada DOI 10.1007/s00024-012-0540-2 Pure and Applied Geophysics Mid-Mountain Clouds at Whistler During the Vancouver 2010 Winter Olympics and Paralympics 1 2 2 2 3 4 RUPING MO, PAUL JOE, GEORGE A. ISAAC, ISMAIL GULTEPE, ROY RASMUSSEN, JASON MILBRANDT, 4 4 1 5 6 RON MCTAGGART-COWAN, JOCELYN MAILHOT, MELINDA BRUGMAN, TREVOR SMITH, and BILL SCOTT Abstract—A comprehensive study of mid-mountain clouds and 1. Introduction their impacts on the Vancouver 2010 Winter Olympics and Pa- ralympics is presented. Mid-mountain clouds were frequently present on the Whistler alpine venue, as identified in an extensive Forecasting orographic cloud poses a great archive of webcam images over a 45-day period from February 5 to challenge in areas of complex terrain where meteo- March 21, 2010. These clouds posed serious forecast challenges rological conditions exhibit dramatic spatial and and had significant impacts on some Olympic and Paralympic alpine skiing competitions. Under fair weather conditions, a diurnal temporal variability (BANTA, 1990;WHITEMAN, 2000; upslope (anabatic) flow can work in concert with a diurnal tem- BARRY, 2008;HOUZE, 2012;GULTEPE et al. 2012). perature inversion aloft to produce a localized phenomenon known During the Vancouver 2010 Olympic and Paralympic as ‘‘Harvey’s Cloud’’ at Whistler. Two detailed case studies in this Winter Games (hereafter referred to as the 2010 paper suggest that mid-mountain clouds can also develop in the area as a result of a moist valley flow interacting with a downslope Olympics), mid-mountain clouds frequently impacted flow descending from the mountaintop. A southerly inflow through the alpine competitions in the Whistler area (see the Sea-to-Sky corridor can be channeled by the local topography Fig. 1). These clouds are locally called ‘‘Harvey’s into a westerly upslope flow toward Whistler Mountain, resulting in orographic clouds on the alpine venue. Under favorable circum- Cloud’’ with reference to a mountain race official and stances, these clouds are trapped to the mid-mountain zone by the weather observer named Harvey Fellowes (JOE et al. leeward subsidence of an elevated southerly flow. The presence of 2010;MAILHOT et al. 2010; also see ‘‘Appendix’’). the downslope subsidence was manifested by a distinguished dry layer observed on the top of the mid-mountain clouds in both cases. However, given the complex terrain in the area, the It is the subsidence-induced adiabatic warming that imposes a underlying mechanisms involved in their formation strong buoyant suppression to trap the mid-mountain cloud. On the and maintenance are not fully understood. This study other hand, the subsidence-induced dry layer has the potential to provides a comprehensive analysis of this low-level trigger evaporative instability to periodically breakup the mid- mountain cloud. orographic cloud, based on the intensive meteoro- logical data available during the 2010 Olympics. The Key words: Mid-mountain clouds, alpine visibility, main goals are to document the mid-mountain cloud orographic flow, evaporative instability. phenomenon, highlight its impacts and the forecast challenges, and provide further insight into its thermal and dynamical origins. The Vancouver Organizing Committee for the 1 National Laboratory for Coastal and Mountain Meteorol- 2010 Olympics (VANOC) contracted with Environ- ogy, Environment Canada, 201-401 Burrard Street, Vancouver, BC V6C 3S5, Canada. E-mail: [email protected] ment Canada (EC) to provide weather services for the 2 Cloud Physics and Severe Weather Research Section, Games (DOYLE et al. 2006;JOE et al. 2010). One of Environment Canada, Toronto, ON, Canada. the greatest challenges faced by EC’s Olympic 3 National Center for Atmospheric Research, Boulder, CO, Forecast Team (OFT) was to accurately predict vis- USA. 4 Recherche en pre´vision nume´rique, Environment Canada, ibility for the downhill ski events on the Whistler Dorval, QC, Canada. alpine venue. Poor visibility due to persistent fog or 5 Pacific Storm Prediction Centre, Environment Canada, alpine cloud was one of the reasons that the Inter- Vancouver, BC, Canada. 6 Monitoring Operations Centre, Environment Canada, national Ski Federation abandoned Whistler as a Richmond, BC, Canada. World Cup venue several years earlier (KINGSTON, 158 R. Mo et al. Pure Appl. Geophys. Figure 1 Topography in the vicinity of Vancouver. Left the greater domain. Right the Whistler area. The locations of the following automatic weather stations are also marked by their identifiers: Whistler Radar (VVO 557 m), Nesters (VOC 659 m), Timing Flats (VOT 805 m), Whistler Creekside (VOB 933 m), Whistler Mt. Mid Level (VOL 1,320 m), Whistler Mt. High Level (VOA 1,640 m), Whistler Mt. High Level Wind (VOH 1,643 m), Roundhouse Helipad (RND 1,856 m), and Whistler Peak (PEK 2,120 m). The Whistler alpine venue ranges from VOT to VOH. The topography data are from the SRTM 300 DEM dataset (FARR et al. 2007) 2010; also see ‘‘Appendix’’). For the 2010 Olympics, forms on the Whistler Mountain slopes under fair the visibility thresholds of alpine competitions were weather conditions. It appears to originate with a set between 200 and 500 m.1 However, with a sparse southerly inflow, and is likely capped by an inversion observational and climatological record in the aloft. This limited knowledge provided the forecast- Whistler area, operational meteorologists do not have ers with a heuristic technique to diagnose and the necessary tools to provide reliable visibility anticipate the cloud. To meet the Olympic forecast forecast with such a degree of precision. requirements, however, the venue meteorologists had The OFT members learned prior to the Olympics to rely on more accurate guidance. A better concep- that severe visibility reduction on the Whistler alpine tual model and a good observing system were also in venue could be expected with heavy precipitation, great demand. blowing snow, or alpine clouds. In particular, the To support mission-critical operations of the OFT, prevalence of Harvey’s Cloud leading to poor visi- EC worked with other partners to establish an bility was recognized during in situ forecasting Olympic Autostation Network (OAN) at a very high exercises in the winters leading up to the 2010 spatial–temporal resolution (DOYLE et al. 2006;JOE Olympics (H. FUNG,A.COLDWELLS,I.DUBE´ ,A. et al. 2010, 2012;GULTEPE et al. 2012). EC also GIGUE` RE, P.-A. BERGERON, and J. GOOSEN, personal developed an experimental high-resolution numerical communications). This mid-mountain cloud often weather prediction (NWP) system for the 2010 Olympics, with customized model outputs, including wind gust and visibility, available for venue fore- 1 During the planning phase of the 2010 Olympics, based on casting (MAILHOT et al. 2010, 2012). In addition, the discussions with sport officials at VANOC, initial visibility thresholds were set as low as 20 m. In the test events in 2009, it World Meteorological Organization conducted a was learned from the International Sport Federation officials that research and development project called the Science the critical visibilities were higher than previously indicated, and of Nowcasting Olympic Weather for Vancouver 2010 the officials needed to know when visibility was forecast to drop below 200 m on all or part of the course, as this could affect event (SNOW-V10), which organized a team of interna- scheduling (C. Doyle, personal communication). tional scientists, including several cloud physics Vol. 171, (2014) Mid-Mountain Clouds Pure and Applied Geophysics 159 experts, to work side-by-side with the OFT on a directly south of the town of Whistler, between research support desk (ISAAC et al. 2012). The project Fitzsimmons Creek and the Cheakamus River, with a also assembled some advanced observational strate- summit elevation of 2,182 m. gies, NWP models, and visualization systems, from All alpine skiing events of the 2010 Olympics which the venue meteorologists benefited greatly for were held on Whistler Mountain at Whistler Creek- their alpine cloud and visibility forecasts. side. The men’s Olympic events took place on the A main goal of the SNOW-V10 project is to Dave Murray Downhill slope, starting at an elevation improve our understanding, and ability to forecast, of 1,684 m. The women’s Olympic events, and all low cloud and visibility in complex terrain (ISAAC Paralympic alpine skiing events, took place on the et al. 2012). This study focuses on the formation of Franz’s Run, starting at an elevation of 1,595 m. Both mid-mountain clouds in the Whistler area, based on courses end at Timing Flats (805 m). This alpine the OAN data and NWP model outputs available for venue is partially protected from southerly winds by the 2010 Olympics. It consists of an overall survey the Khyber Cliff that forms the north side of the and two detailed case studies. The results can be used Cheakamus River. It is prone to the southwest inflow to set forth a conceptual framework for the opera- through the valley and, to a lesser extent, to the tional forecast of mid-mountain clouds in the northerly outflow as well. Whistler area. Such a conceptual model is also expected to have a broader impact on the study of 2.2. The Olympic Autostation Network Data orographic clouds in complex terrain, and can be applied to predict mid-mountain clouds and the Data from a variety of weather observing systems associated weather in other areas with similar geo- installed in the Whistler area are used in this study. graphical features. These include data from eight OAN automatic The remainder of the paper is organized as fol- stations (Fig. 1), located at Nesters (VOC), Timing lows. Section 2 describes the topographical features, Flats (VOT), Whistler Creekside (VOB), Whistler OAN data, and EC’s NWP models.