Poland is situated in a moderate climate zone, which determines its climate as continental with warm summers, crisp, sunny autumns and cold winters. The climate is chiefly shaped by air masses that come over the territory. In summer, humid polar-maritime air from the north Atlantic brings clouds, precipitation and cold weather, whereas in winter it causes thaw and fog. Relatively dry polar-continental air from Russia, which typically comes to Poland in winter, brings frosts while in summer it is responsible for heat periods. Arctic air from far north (the Arctic Sea) produces changeable weather and sudden temperature drops such as freezes in May.
In summer (July) the average temperature amounts to 19 degrees Celsius. However, there are sultry days with thermometer peaking as high as 30 degrees. The coolest months are January and February with temperatures falling a couple of degrees below zero. Snow covers especially the mountainous area (in the south) from the middle of December to April.
The average mean temperature in Warsaw range is from -6° to -1°C (21-30°F) in January and from 13° to 24°C (55-75°F) in July. Precipitation is greatest during the summer months, lasting 85 to 100 days. Annual rainfall ranges from about 50 cm (20 in) in the lowlands and 135 cm (53 in) in the mountains; the overall average is about 64 cm (25 in).