So, how hot does it really have to be? Most districts look at a number called the heat index, not just the raw thermometer reading. Think of the heat index as the “feels like” temperature when you add in humidity.
If the air is thick and soupy, your body can’t cool itself by sweating. A dry 95°F might be a bummer, but a humid 90°F can feel like walking through a wet blanket. That’s when schools start paying attention.
Generally, many districts will cancel school if the heat index is expected to hit 100°F to 105°F or higher, especially early in the day. But here’s the kicker: it depends on your local climate.
The “Arizona vs. Minnesota” Problem
Imagine a school in Phoenix, where it’s 110°F in the shade. They’re used to it—air conditioning is everywhere. Now imagine a school in coastal Maine hitting 92°F with 90% humidity. That’s a different story.
What’s a light breeze in the desert can be a dangerous, sticky haze in a place without AC. Schools in cooler climates might cancel for heat waves that would be just a “warm Tuesday” in the South. Fun, right?
This is why there’s no national “one number fits all.” It’s about infrastructure, not just the weather. Do classrooms have fans? Is the gym air-conditioned? If not, a 90°F day can be a big problem.
Petition · Cancel school tomorrow · Change.org
