Georgia is divided into separate climatic regions because of the Chattahoochee River. The mountain region to the northwest is colder than the rest of Georgia, averaging 39°F (4°C) in January and 78°F (26°C) in July. The state experiences mild winters that range from a January average of 44°F (7°C) in the piedmont to 54°F (12°C) on the coast. Summers are hot in both these regions with July temperatures averaging 80°F (27°C) or above. Humidity is high, ranging from 82% in the morning to 56% in the afternoon in Atlanta. Georgia receives an average annual rainfall of 50 inches in the lowlands to 75 inches in the mountains. Tornadoes are an annual threat in mountain areas, and Georgia beaches are exposed to hurricane tides.