diurnal shift

A fancy term that describes the variation in temperature from highs during the day to lows at night. This is particularly relevant to wine regions at high altitudes because they experience the most dramatic temperature swings. Large temperature variations affect the grapes because their exposure to sunlight increases the ripening qualities in the wine (i.e. more sugar), while the sudden drop in temperature at night preserves the balance of natural acids in the grape (i.e. lots of acidity in the wine).