The United States of America, with its size of almost 10 million km² and a wide variety of landscapes, extends over numerous climate zones. Northern Alaska has an arctic climate with temperatures up to 30°C below zero, while most of the land mass of the USA is in a continental temperate climate zone. A completely different climate prevails in the southern sun states. While the Californian Pacific coast is relatively mild and Mediterranean with an annual average temperature of 17 °C, the Californian deserts and mountains already have significantly higher temperatures. All in all, it is warm all year round in all southern states.
On the opposite side of the USA on the Atlantic coast of Florida the temperatures are noticeably higher again, but the rainy days are also more numerous. Here the climate is determined by the Atlantic currents and in the summer months it is the rainy season. While spring is the driest time in Florida, autumn can be quite unpleasant with its hurricanes. It has a tropical climate.
In the interior, the up to 4400 meters high Rocky Mountains share a large part of the country. The mountain range running in north-south direction also separates climatic regions from each other. In the west of the Rocky Mountains, rain-rich low pressure areas are formed, which bring cool air masses from the Pacific and cause frequent rainfalls. On the eastern side, on the other hand, there is often drought at higher temperatures and lower humidity.
In contrast to Europe, there is no East-West mountain range in the USA. The Rocky Mountains separate the more western parts of the country from Pacific weather influences. However, cold currents from the north and warm air masses from the south can move almost unhindered through the country. Thus, larger cold air infiltrations are to be felt up to the southernmost regions.
Last but not least, the USA has 4 large desert areas far away from the coasts (Chihuahua, Mojave, Sonora Desert and Great Basin Desert), which rarely consist of Saharan-like sand landscapes, but nevertheless have their individual mesoclimatic characteristics and vegetations. Famous is the Death Valley in the Mojave Desert, where it gets hot up to 50°C during the day.
› Duration of daylight and sunshine in the United States
hours of sunshine per day rainy days per month Precipitation in mm/day Relative humidity in % Water temperature Absolute humidity in g/m³ (approx.)
Long-term development of temperatures from 1979 - 2018
In the years 1979 to 2018 there were only 25 weather stations in the whole country, which reported continuous temperature values. From these weather reports we have created a long-term development that shows the monthly average temperatures. The hottest month in this entire period was Juli 2018 with 24.6 °C. Januar 1979 was the coldest month with an average temperature of -1.0 °C.
The average annual temperature was about 12.8 °C in the years after 1979 and about 14.0 °C in the last years before 2018. So in less than 40 years it has increased by about 1.2 °C. This trend only applies to the selected 25 weather stations in the United States. A considerably more comprehensive evaluation of the global warming
has been provided separately.