The Barossa Valley has a Mediterranean climate, but its transverse valleys and sloping hills create a wide range of micro climates. Temperatures vary from very warm on the valley floors to progressively cooler at higher altitudes on the hillsides and further east in the valley. Despite the Barossa Valley's reputation as a warm region, much of its climate is similar to the relatively cooler Margaret River area in Western Australia – though the Barossa has a wider diurnal temperature range.
During the October to April growing season, the region receives about 1710 heating degree days, mean average temperatures during the crucial ripening month of January being around 70°F (21.4°C). Rainfall during the growing season averages only around 6.3 inches (160mm), with average relative humidity around 39 per cent, which means irrigation is often necessary. Many of the old vine vineyards on the western side of the valley are an exception, and are often dry-farmed without irrigation.