Final answer:
Off-piste ski areas are prepared to provide safe and challenging skiing experiences. The snow can remain on slopes above freezing due to the albedo effect and nocturnal refreezing. Surveys on the best U.S. skiing spots relate to statistics and require analysis to understand relationships between ski area preference and skier level.
Step-by-step explanation:
Off-piste ski areas are prepared in mountain regions to provide a skiing experience that is different from groomed slopes. In off-piste skiing, participants get to ski on unmarked and not patrolled areas. These areas require preparation to ensure safety as they may be prone to avalanches, and to offer challenging yet enjoyable terrain for the experienced skiers. The condition that snow can remain on slopes despite temperatures being above freezing is due to a phenomenon called albedo effect. This is where the snow reflects a large amount of solar radiation, thus lessening the degree of melting. Additionally, nocturnal refreezing can occur, where temperatures drop below freezing at night, reinforcing the snowpack.
The question of where the best skiing is in the U.S. and how it relates to the skill level of the skier addresses the subject of statistics, and a survey or experiment would be used to test the independence between perceived best ski area and skier level. This employs concepts such as chi-square tests or other statistical analyses to understand the potential relationships or biases in the survey responses.