In general the Barossa Valley has a continental climate but its series of transverse valleys and sloping hills does produce a wide range of meso climates. Temperatures vary from very warm on the valley floors to progressively cooler at higher altitudes on the hillsides and further North in the valley. Despite its reputation as a "warm climate region", main of the Barossa Valley's climate figures are not that dissimilar from the relatively cooler Margaret River in Western Australia-though the Barossa does have a wider diurnal temperature range. During the heat summation and mean temperatures during the October to April growing season, the region receives about 1710 heating degree days with 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%, which means that viticultural irrigation is often used. The exception is many of the old vine vineyards on the slightly cooler western side of the valley which is often dry-farmed without irrigation
