Ski resorts across the country are using the Thanksgiving weekend to jump start their winter seasons, but with every passing year comes a frightening realization: If global temperatures continue to rise, fewer and fewer resorts will be able to open for the traditional beginning of ski season. Warmer temperatures at night are making it more difficult to make snow and the snow that falls naturally is melting earlier in the spring. In few places is this a bigger concern than the American West, where skiing is one of the most lucrative segments of the tourism industry and often the only...