Climatically, most of Bulgaria is part of the temperate continental zone but for the southernmost areas that are part of the continental Mediterranean sub zone of the subtropical zone and anything typical of the countries of Central and Western Europe is to be observed there: the movement of humid and relatively warm air currents from the Atlantic Ocean and the cold winds from the Arctic Ocean. The Balkan Range is a shield against this cold air and the winter temperatures in Northern Bulgaria are lower than elsewhere in the country. The Mediterranean climatic influence is felt mostly in the basins of the rivers Maritsa, Toundja, Strouma and Mesta that are the funnels letting in the warm and humid air from the Aegean Sea. At the seaside the summer is warm but not hot and the winter is mild. The lowest mean temperatures in Bulgaria of minus 2°C are recorded in January in North Bulgaria, in the vales sandwiched between the Balkan Range and Sredna Gora Mountains and in the high-altitude fields in Southwest Bulgaria. The highest mean temperatures of 32°C are recorded in July and August in the Upper Thracian Plain.