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Mid-Mountain Clouds at Whistler During the Vancouver 2010 Winter Olympics and Paralympics |
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| Authors: | Ruping Mo Paul Joe George A Isaac Ismail Gultepe Roy Rasmussen Jason Milbrandt Ron McTaggart-Cowan Jocelyn Mailhot Melinda Brugman Trevor Smith Bill Scott |
| Institution: | 1. National Laboratory for Coastal and Mountain Meteorology, Environment Canada, 201-401 Burrard Street, Vancouver, BC, V6C 3S5, Canada 2. Cloud Physics and Severe Weather Research Section, Environment Canada, Toronto, ON, Canada 3. National Center for Atmospheric Research, Boulder, CO, USA 4. Recherche en prévision numérique, Environment Canada, Dorval, QC, Canada 5. Pacific Storm Prediction Centre, Environment Canada, Vancouver, BC, Canada 6. Monitoring Operations Centre, Environment Canada, Richmond, BC, Canada |
| Abstract: | A comprehensive study of mid-mountain clouds and their impacts on the Vancouver 2010 Winter Olympics and Paralympics is presented. Mid-mountain clouds were frequently present on the Whistler alpine venue, as identified in an extensive archive of webcam images over a 45-day period from February 5 to March 21, 2010. These clouds posed serious forecast challenges and had significant impacts on some Olympic and Paralympic alpine skiing competitions. Under fair weather conditions, a diurnal upslope (anabatic) flow can work in concert with a diurnal temperature inversion aloft to produce a localized phenomenon known as “Harvey’s Cloud” at Whistler. Two detailed case studies in this paper suggest that mid-mountain clouds can also develop in the area as a result of a moist valley flow interacting with a downslope flow descending from the mountaintop. A southerly inflow through the Sea-to-Sky corridor can be channeled by the local topography into a westerly upslope flow toward Whistler Mountain, resulting in orographic clouds on the alpine venue. Under favorable circumstances, these clouds are trapped to the mid-mountain zone by the leeward subsidence of an elevated southerly flow. The presence of the downslope subsidence was manifested by a distinguished dry layer observed on the top of the mid-mountain clouds in both cases. It is the subsidence-induced adiabatic warming that imposes a strong buoyant suppression to trap the mid-mountain cloud. On the other hand, the subsidence-induced dry layer has the potential to trigger evaporative instability to periodically breakup the mid-mountain cloud. |
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