A heat wave is a stretch of unusually hot weather that lasts for several days or longer. It matters because heat can stress the human body, damage crops, raise electricity demand, and worsen air pollution. Heat waves often happen when a strong high-pressure system parks over a region and stays there.
This high-pressure area acts like a heat dome, keeping hot air trapped near the ground.
Inside a heat dome, sinking air is compressed by the weight of the atmosphere above it, and compressed air warms. The sinking motion also reduces cloud formation, so more sunlight reaches the ground and heats roads, roofs, soil, and buildings. Weak winds prevent cooler air from moving in, so each day can start warmer than the last.
Climate change raises average temperatures, which makes extreme heat events more frequent, longer lasting, and more intense.
Key Facts
- A heat wave is usually defined as several days of temperatures much higher than normal for a specific place and season.
- High pressure causes air to sink, and sinking air warms by compression.
- Compression heating follows the idea that increasing pressure on a gas can increase its temperature.
- Heat domes reduce cloud formation, so incoming sunlight increases surface heating.
- Heat waves can produce temperatures about 10 to 20°F above normal for multiple days.
- Temperature conversion: °C = (°F - 32) × 5/9 and °F = (°C × 9/5) + 32.
Vocabulary
- Heat wave
- A heat wave is a period of unusually hot weather that lasts for several days or more in a specific region.
- High-pressure system
- A high-pressure system is an area where air pressure is higher than surrounding areas and air tends to sink.
- Heat dome
- A heat dome is a persistent high-pressure pattern that traps hot air near the surface like a lid.
- Compression heating
- Compression heating is the warming of air as it sinks and is squeezed by higher pressure closer to the ground.
- Urban heat island
- An urban heat island is a city area that stays warmer than nearby rural areas because pavement, buildings, and roads absorb and release heat.
Common Mistakes to Avoid
- Thinking one hot afternoon is always a heat wave, which is wrong because heat waves require unusually high temperatures lasting for several days or more.
- Assuming high pressure means cooler weather, which is wrong because sinking air under high pressure can warm by compression and reduce cloud cover.
- Ignoring nighttime temperatures, which is wrong because warm nights prevent people, buildings, and roads from cooling down and increase health risks.
- Saying climate change causes every single heat wave by itself, which is wrong because weather patterns trigger events, while climate change raises the background temperature and makes extreme heat more likely.
Practice Questions
- 1 A city normally reaches 86°F in July, but during a heat wave it reaches 101°F for four days. How many degrees Fahrenheit above normal is the temperature?
- 2 Convert 104°F to degrees Celsius using °C = (°F - 32) × 5/9.
- 3 Explain why a high-pressure heat dome can make a heat wave worse even when no new hot air is moving into the region.