The sticky truth about dew point and relative humidity
Important safety tips to help you beat the heat
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We’ve all heard the classic line, “It’s not the heat, it’s the humidity.” But honestly, what is humidity? And what exactly does dew point measure? Let’s dive into the sticky, sweaty truth behind these weather terms.
Dew points
Summers in Minnesota can get hot, but it’s when the dew points climb into the 60s and 70s that we really start to feel the difference.
The dew point is the temperature at which the air becomes fully saturated with moisture, causing water vapor to condense into dew, fog, or clouds. Simply put, it’s a direct measure of how much moisture is in the air.
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The higher the dew point, the more moisture there is in the air. The scale below shows the dew point ranges when the weather starts to feel a bit uncomfortable outside.
Because dew point is based on actual moisture content, it gives a more accurate sense of how "humid" it really feels outside. This is why meteorologists prefer the dew point—it’s a more accurate measure of how uncomfortable or sticky the air will feel.
Relative humidity
Relative humidity (R), on the other hand, is a percentage that compares the current amount of moisture in the air to the maximum amount the air could hold at that temperature.
For example:
100% relative humidity means the air is fully saturated (likely foggy or raining).
50% RH means the air is holding half the moisture it could at that specific temperature.
But here's the catch with relative humidity, it depends on temperature. Warm air can hold more moisture than cool air. That means on a hot day, 50 percent relative humidity can feel very humid, while on a cold day, the same 50 percent can feel quite dry.
Why it’s hard to stay cool in humid conditions
When the air is humid, especially with a high dew point, your sweat can’t evaporate as easily. And since evaporation is how your body cools down, you end up feeling hotter, stickier, and more uncomfortable.
Tips for staying safe in the heat
Staying safe in the heat is important to prevent heat-related illnesses. Here are a few key tips to help keep you cool:
Drink plenty of water and avoid alcohol and caffeine.
Limit time outdoors during the hottest parts of the day.
Wear light, loose clothing and use sun protection
Stay in air-conditioned places when possible, or use fans to help cool down.
Take breaks and rest often if you’re active outside.
