Diurnal Temperature Fluctuation
The difference in temperature between the warmest part of the day and the coolest part of the night. A large diurnal temperature fluctuation is ideal for grapes since it allows the sugars to ripen during the heat of the day while the natural acids are preserved thanks to the coolness of the night. Washington state has one of the largest diurnal fluctuations of any wine region, often with daytime highs around 92o F and nighttime lows of 45 o F.