The weather behind every vintage

Heat makes the vintage, rain decides the harvest

Grapevines grow when it is warmer than about 10°C. Add up how far each day's mean temperature sat above that line through the growing season and you get growing degree days (GDD), the measure viticulturists have used since Amerine and Winkler mapped California's vineyards in 1944. Cool regions such as the Mosel or Champagne collect around 1,100–1,200; Jerez and the Hunter Valley more than twice that.

A season that runs far above its region's normal pushes ripening early, and one far below can struggle to ripen at all. Rain in the weeks before picking brings rot and dilution. This site shows those numbers for each vintage, and nothing more. It is not a quality rating.