What Causes a Heat Wave? Why Temperatures Get So High
Have you ever stepped outside and felt like you walked straight into an oven? Not just hot, really hot, day after day, with no break? That’s a heat wave. And the wild part is, it’s not just “extra sun.” Something is actually trapping the heat in place, like a lid on a pot.
Here’s what’s going on, and why heat wave temperatures can climb so much higher than a normal summer day.
What is a heat wave, exactly?
A heat wave is a stretch of days, usually three or more, where the temperature is much hotter than what’s normal for that place. If a city is usually around 80°F in summer, a heat wave could push it to 95°F, 100°F, or higher, for days in a row.
It’s not about one hot afternoon. It’s about the heat sticking around and refusing to leave.
So why does it get stuck?
Picture a big, heavy blanket of air parking itself over a city and just… staying there. That’s basically what a heat wave is. Scientists call it a “heat dome,” and here’s how it forms:
A large area of high-pressure air settles in and barely moves for days or even weeks. That high-pressure air acts like a lid on a pot of boiling water, it pushes warm air down and traps it close to the ground.
That same lid also pushes clouds away. No clouds means nothing is blocking the sun, so its rays hit the ground directly, heating up the air even more. The hot air gets squeezed under the dome with nowhere to go, so it just keeps building.
Why does it feel even hotter than the number on the thermometer?
This is the part most people don’t expect: humidity makes heat feel worse than the actual temperature suggests.
Your body cools itself by sweating, when sweat evaporates off your skin, it carries heat away with it. But if the air is already full of moisture (high humidity), your sweat can’t evaporate as easily. It just sits there. Your body’s cooling system basically stalls out.
That’s why a 95°F day with high humidity can feel more brutal than a 100°F day in dry air.
Why kids need extra care during a heat wave
Kids heat up faster than adults do. Their bodies produce more heat relative to their size, but they sweat less efficiently, so they can’t cool down as quickly. That’s a real, physical difference, not just a parenting worry.
A few things that actually help:
- Push outdoor playtime to early morning or evening, when it’s cooler.
- Keep water within reach, don’t wait for “I’m thirsty” before offering it.
- Loose, light-colored clothing breathes better than anything tight or dark.
- Watch for flushed skin, dizziness, or a kid who suddenly seems extra cranky or tired, those can be early heat signs, not just a bad mood.
If a kid stops sweating, seems confused, or their skin feels hot and dry to the touch, that’s not a “wait and see” situation, get them cooled down and call your pediatrician.
Are heat waves becoming more common?
Yes, and this is worth knowing, not to scare anyone, but because it explains what you’re seeing on the news more often. As the planet’s average temperature rises, heat waves are showing up more frequently and lasting longer than they used to. The heat dome itself isn’t new; there are just more of them, and they’re sticking around longer.
The short answer
A heat wave happens when a dome of high-pressure air parks itself over an area, traps warm air near the ground, and blocks the clouds that would normally cool things down. Add humidity, and it feels even hotter than the thermometer says.
Next heat wave that rolls through, you’ll know exactly what’s happening over your head, and why it’s smart to keep the water bottles full and the outdoor play scheduled for cooler hours.
For more on what’s happening in the sky, check out what clouds are and what the atmosphere is, both explain the layers that make heat waves (and every other kind of weather) possible. You can also browse more weather explained posts for kids.
