There are a few important things to note about the data in the chart. The Average Monthly Mean Temperature regulates the vine’s metabolism. Warmer temperatures lead to more rapid grape maturation. This is the most important measure when considering the suitability of a grape variety for a given site. While the average high temperature is interesting, in less humid climates like California the period of the day when this temperature is reached is often very brief. In most California vineyards the mean temperature is only 40-45% of the difference between the high and the low, meaning that the mean is closer to the low than the high. Meanwhile in more humid European climates the mean temperature is often closer to 60% of the diurnal (i.e. closer to the high).
It is important to note that we don’t have actual Monthly Mean Temperature data for several of the sites below. In some cases it is just an average of the high and the low. Also, the data from our estate Vineyards is derived from the most recent 5-10 vintages. During this period, California has experienced much warmer Septembers than historical averages. Some speculate that this due to climate change in our area.
