The climate in the United States

vgwortAverage daytime and nighttime temperatures

All climatic diagrams of this page are taken from the collected data from 398 measuring stations in the United States.
Weather stations at an altitude above 2300m have not been included.
All data correspond to the average monthly values of the last 20 years.

Back to overview: United States

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
Sunshine hours per day in the United States
rainy days per month
Rainy days per month in the United States
Precipitation in mm/day
Precipitation in the United States
Relative humidity in %
Relative humidity in the United States
Water temperature
Water temperatures in the United States
Absolute humidity in g/m³ (approx.)
Absolute humidity in the United States

Temperature records of the last 70 years

The hottest temperature measured from 1949 to March 2019 was reported by the Montgomery Al weather station. In June 2007 the record temperature of 54.4 °C was reported here. The hottest summer from July to September, based on all 309 weather stations in the United States below 2300 metres altitude, was recorded in 2019 with an average temperature of 23.2 °C. This average temperature will normally be measured every 4 to 6 hours, thus also including the nights. Normally, this value is 21.6 degrees Celsius. The average maximum daily temperature at that time was 29.2 °C.

The coldest day in these 70 years was reported by the weather station Mc Grath Ask. Here the temperature dropped to -51.9 °C in February 1999. Mc Grath Ask lies at an altitude of 103 meters above sea level. The coldest winter (January to March) was in 1971 with an average temperature of 0.1 °C. In the United States, it is usual to have about 3.1 degrees more at 3.2 °C for this three-month period.

Langzeitentwicklung der Temperaturen von 1979 - 2019

Anders als bei einzelnen Rekordwerten kann man eine Langzeitentwicklung nicht einfach über alle Wetterstationen des Landes herbeiführen. Sowohl die Anzahl als auch die Standorte ändern sich ständig. Ein simpel errechneter Durchschnittswert würde ein verfälschtes Ergebnis ergeben. Kommen in einem Jahr mehrere Messstationen in besonders kalten Berg- oder Küstenregionen hinzu, würde der Durchschnitt allein hierdurch bereits sinken. Fällt eine Station über die Sommer- oder Wintermonate aus, liefert sie keine Werte und verfälscht den Schnitt erneut. Die nachfolgende Langzeitentwicklung wurde daher auf nur 25 Messpunkte reduziert, um über einen möglichst langen Zeitraum tatsächlich vergleichbare Daten zu haben.

In den Jahren 1979 bis 2019 gab es im ganzen Land nur diese 25 Wetterstationen, die durchgehend Temperaturwerte gemeldet haben. Aus diesen Wetterberichten haben wir eine Langzeitentwicklung erstellt, die die monatlichen Durchschnittstemperaturen darstellt. Der heißeste Monat in diesem gesamten Zeitraum war der 2018 mit 24.6 °C. Der 1979 war mit durchschnittlichen -1.0 °C der kälteste Monat.

Die Jahresdurchschnittstemperatur lag in den Jahren nach 1979 bei ungefähr 12.8 °C und in den letzten Jahren vor 2019 bei rund 14.0 °C. Sie hat sich also in weniger als 41 Jahren um ungefähr 1.2 °C erhöht. Diese Tendenz gilt allerdings nur für die ausgewählten 25 Wetterstationen in the United States. Eine erheblich umfangreicher angelegte Auswertung des globalen Temperaturanstiegs haben wir separat zur Verfügung gestellt.

Long-term development of temperatures in the United States

More detailed information on global warming with a view by continent can also be found on our topic page on climate change.