An omega block forms when a high-pressure system becomes trapped between two low-pressure systems.
The pattern prevents weather from moving on, allowing heat to build for days or even weeks.
Climate change is making heatwaves more intense, amplifying the impact of such weather events.
Western Europe is once again in the grip of an intense heatwave, with countries including France, the United Kingdom, Italy and the Netherlands recording unusually high temperatures. The extreme weather has disrupted daily life, forcing school closures, interrupting public transport and prompting authorities to open air-conditioned public spaces to vulnerable residents.
More than 40 people have drowned in France over the past week after seeking relief from the heat in unsupervised waters. The country recorded its hottest day since records began in 1947, with temperatures reaching 44.3 degrees Celsius. Thousands of homes have also been left without electricity amid the heatwave. Across Europe, governments have issued extreme heat warnings as temperatures continue to soar.
Meteorologists say the prolonged heat is being driven by a weather phenomenon known as an omega block.
What Is An Omega Block?
An omega block is named after the Greek letter Ω because of the distinctive shape it creates in the atmosphere. It forms when a large area of high pressure becomes trapped between two low-pressure systems on either side.
Under normal conditions, the jet stream pushes weather systems steadily from west to east. During an omega block, however, the jet stream becomes distorted and buckles dramatically north and south, isolating the pressure systems. Weaker steering winds and reduced temperature contrasts in the atmosphere can contribute to these slow-moving patterns.
The high-pressure system effectively becomes stuck in place, preventing weather from moving through the region as it normally would. As a result, the same conditions can persist for days or even weeks. Most omega blocks last between three and ten days, but some have been known to endure much longer.
Why It Traps Hot Air For Days
The centre of an omega block is dominated by high pressure, which creates hot, dry and stable conditions. High pressure suppresses cloud formation, resulting in clear skies and prolonged sunshine that allow temperatures to rise steadily.
These are the conditions currently affecting parts of France and Spain, where temperatures have climbed above 40 degrees Celsius. With little cloud cover and no significant weather systems moving through, the heat remains trapped over the same areas day after day.
Meanwhile, the low-pressure systems on either side of the omega block experience very different weather. These regions are more likely to receive cooler temperatures, cloud cover and rainfall. Britain currently sits near the boundary between the hot high-pressure system and cooler air to the northwest, creating a sharp contrast between hotter conditions in the south and east and cooler, wetter weather in the north and west.
Why Europe Is Struggling More Than India
Unlike many tropical regions, European cities were historically built to retain warmth rather than cope with prolonged extreme heat. As a result, many homes and public buildings can become heat traps during severe heatwaves.
Air conditioning remains far less common in Europe than in other parts of the world. While nearly 90 per cent of homes in the United States have air conditioning, only around 20 per cent of European homes do. For decades, much of Europe simply did not experience sustained periods of extreme heat frequently enough to justify widespread cooling systems.
This has contributed to a culture in which air conditioning has often been viewed as a luxury rather than a necessity. Higher energy costs in many European countries have also discouraged widespread adoption. As a result, many residents rely on electric fans, cold showers and other temporary measures to cope with heatwaves.
Some southern European regions have traditionally adapted to warmer climates through architecture. Thick walls, smaller windows and designs that maximise airflow help keep buildings cooler naturally. However, in many parts of northern and western Europe, homes were not designed with rising temperatures in mind, leaving residents especially vulnerable during prolonged heat events.
Is Climate Change Making It Worse?
Scientists have not yet reached a consensus on whether climate change is directly increasing the frequency of omega blocks and other atmospheric blocking events.
What is clear, however, is that climate change is making heatwaves more intense. Human activities, particularly the burning of coal, oil and gas, have warmed the planet by about 1.3 degrees Celsius since pre-industrial times.
This higher baseline temperature means that when heatwaves occur, they start from a warmer point and reach more extreme levels. According to climate scientists, European heatwaves are now between two and four degrees Celsius hotter than they would have been without human-caused warming.
As a result, when weather patterns such as omega blocks develop, they can produce significantly more dangerous temperatures than they did in the past.
Could India Face Similar Weather Patterns?
India can experience atmospheric blocking patterns that trap weather systems over a region for extended periods, although they typically interact with different climatic forces than those affecting Europe. While omega blocks are most commonly associated with the mid-latitudes of Europe and North America, prolonged high-pressure systems can also contribute to persistent heatwaves in parts of India.
As global temperatures continue to rise, scientists expect extreme heat events to become more intense, meaning any weather pattern that stalls over a region could have more severe impacts than in the past.
