But you step onto the asphalt, and within ninety seconds your shirt is stuck to your back.
That something has a name: the heat index.
It's the number that explains why a perfectly ordinary summer day can put you in the emergency room — and why the official temperature is lying to your body, even when it isn't lying to you.
Your body cools itself by sweating, and sweat only works if it can evaporate.
When humidity is low, that moisture leaves your skin fast and you feel fine.
When humidity is high, the air is already crowded with water vapor.
So your body keeps heating up, and the air keeps lying about how hot it really feels.
The heat index is the temperature your body actually experiences once you factor in that humidity.
An 88-degree day at 75 percent humidity doesn't feel like 88.
That's the number the National Weather Service publishes, and it's the number that correlates with heat stroke, not the one on the thermometer.
Americans have quietly built their lives around ignoring this.
We schedule little league games at noon in July.
We send warehouse workers into unairconditioned buildings with a Gatorade and a nod.
We tell ourselves we're tough because our grandparents didn't have AC, forgetting that our grandparents also died of "summer complaint" in numbers we no longer bother to count.
Last year, heat killed more Americans than hurricanes, tornadoes, and floods combined — and most of those deaths weren't dramatic.
They happened in apartments, in cars, in beds, alone.
The cruelty of the heat index is that it punishes the people least able to escape.
The elderly in brick buildings without central air.
The kid at football practice whose coach says "hydrate up" and means it as a full safety plan.
The unhoused man on a bench who nobody checks on until the news does a segment in August.
And here's the part that should unsettle you: the index is climbing.
As the climate warms, humidity is rising with it, which means the same 95-degree day that felt like 100 in 1985 feels like 110 now.
Cities are quietly installing cooling centers and heat officers, which is bureaucrat-speak for "we know people will die and we're trying to slow it down." None of this requires panic.
Check the heat index, not the temperature, before you plan your run.
Check on the neighbor with the window unit.
Treat a 105 heat index the way you'd treat a snowstorm — as a day that changes what's safe.
The thermometer tells you what the air is.
The heat index tells you what it's doing to you.
Only one of those numbers has ever killed anybody.
We spent a century air-conditioning our way out of summer, and we convinced ourselves the problem was solved.
It was deferred, and the bill is arriving in degrees that don't match the number on the screen.
Final Thoughts
The least we can do is learn to read the real one.