Rheinhessen is one of the four large drylands in Germany and is one of the sunniest and driest regions in Central Europe. Apart from the southwest of the region, the annual precipitation varies on average between 400 and 500 mm, which is low for German conditions. Hunsrück and Pfälzer Bergland (Donnersberg) keep the damp westerly winds off, "the rain remains in the mountains," which also provide wind protection, and the incoming sea-air masses rise warmly, but with little rain, to Rheinhessen. The clouds dissolve and bring only low rainfall. Larger rains are almost exclusively due to cloudbursts and summer thunderstorms. Rheinhessen also has the highest sunshine duration of all German wine-growing regions (almost 1600 hours). Oppenheim is after Freiburg i.Br. the »hottest wine-growing city in Germany« (mean temperature of 9.8 ° C). Winter and autumn are generally mild. On the other hand, autumn is coming rather late. This results in a vegetation period of about 240 days. Here, too, Rheinhessen is unmatched by any other German wine-growing region, a fact that is significant for the maturity of the grapes.