Outlook International Desk
A heat dome refers to an exceptionally hot air mass trapped by high pressure aloft, preventing the warm air below from rising. This phenomenon results in clear skies, as the sinking air warms during its descent. Clouds typically form under opposite conditions, where rising air cools and condenses into water droplets.
High-pressure conditions associated with heat domes lead to increased sunshine, further warming the air and drying out the soil. This reduced soil moisture decreases evaporation, resulting in fewer clouds and rain. Such positive feedback loops can cause increasingly hotter conditions the longer the heat dome remains in place.
Jet streams are fast-flowing bands of wind in the upper atmosphere that move weather systems across the planet. Occasionally, these jet streams form large loops, causing weather systems to become trapped in these loops, known as blocking patterns. This can lead to prolonged periods of extreme weather, including heat domes.
Heat domes can persist from a few days to several weeks. For example, a significant heat dome over Canada and the northwest United States in 2021 lasted nearly a month, with temperatures reaching nearly 50°C (122°F) in British Columbia, the highest ever recorded in Canada.
While heatwaves are becoming more frequent due to climate change, specific studies on heatwaves caused by heat domes are limited. There is ongoing debate about how global warming affects the blocking patterns that trap heat domes. A 2023 study suggested an increase in "summer heat-dome-like stationary waves" over northwestern North America.
Heat domes are becoming hotter as the global temperature rises. The world is nearly 1.5°C warmer than in preindustrial times, causing today's heat domes to produce higher surface temperatures than previously.
NWS advises people to stay indoors, drink more fluids, and avoid going out unless it’s necessary. Long exposure to sun during heatwaves or heat domes may lead to fatigue, heat cramps, and heat strokes. People are advised to stay in cooler places and keep themselves cool by wearing light clothes and consuming more fruits and liquids.
While next-day weather forecasts are generally accurate, predictions become less reliable further into the future. Dangerous heat levels are expected across many areas of the contiguous United States in the coming week.