Geography and urban development of Dresden temperatures are almost the same as those in cities in southwest Germany; on average 10.2°C per year. In hot summers, Dresden is between the hot Lusatia and the milder Ore Mountains. Both regions are characterised by strong winters: temperatures of −20°C are not impossible in Dresden. The driest months are February and March, with precipitation of 40 mm. Spring months have often been arid in the last couple of years (with less than 10 mm of precipitation). The most precipitation falls in July and August, at 60 mm per month. Due to its location on the banks of the Elbe
Accession of Hamburg to the German Customs Union (Zollverein) form a wider more powerful entity. The states which joined fought vigorously against any impairment of their full sovereignty. Hence each member had a veto and the union was not permanent, but had to be renewed after 12 years. Each member sought its own economic advantage. Accordingly, the accession of any of the Hanseatic cities of Hamburg, Bremen or Lübeck would have to be on condition that accession served the city's own advantage. A pre-condition of such advantage was that their territory touched directly with that of the Customs Union, which only happened for Hamburg after 1854, when Hanover joined.