A distinct high-pressure system over the southern United States, better known as "Heat Dome", has threatened millions of inhabitants with unbearable heat for days. In the country's south, the daily maximum temperatures have reached 40°C in some locations.

At the beginning of this week, Johannesburg, South Africa, experienced the first snowfall in 12 years. In the Northern Hemisphere, however, record-breaking high temperatures can be observed, particularly in the southern USA. Subsequently, the authorities have issued warnings of extreme heat over large areas, as visualised on our weather warning map.

The reason for the long-lasting and intense heat is the formation of a heat dome. This is a weather phenomenon in which a stationary area of high pressure (a “dome” in this case) traps heat in one place. Further air masses flowing into this area are then also heated by adiabatic compression, increasing the temperatures even higher.

The extremely high temperatures can be seen clearly on our maximum temperature map, and our forecast for the next few days. You can also use our measured temperature map showing measured data for the past and current time steps. In the next few days, the states of Nevada, Arizona and California will be particularly affected by the enormous heat. For Phoenix (Arizona), temperatures of 47°C are expected in the upcoming days.

Decreasing temperatures can only be expected when the stable area of high pressure weakens. Until then, avoiding the heat as much as possible is important, for which our city-specific heat maps can be consulted. They show a two-dimensional temperature field for over 80 cities worldwide. With the help of these maps, you can locate cooler places in the cities. Explore the cooling effect of urban green spaces in your area, and stay cool!