Why meteorologists love using dew point and ignore relative humidity
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As meteorologists, one of the questions we hear all the time is: “Why don't you talk about relative humidity?” After all, it's the humidity number most people see on weather apps and forecasts.
The answer is simple: relative humidity doesn't tell the whole story.
Dew point vs. relative humidity
Relative humidity depends on temperature. As the air warms during the day, the relative humidity can drop even though the amount of moisture in the air hasn't changed at all. That's why a summer afternoon can feel incredibly sticky while the relative humidity appears surprisingly low.
That's where dew point comes in. Dew point measures the actual amount of moisture in the air, making it a much better indicator of how humid and uncomfortable it feels outside.
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Monday was a perfect example of why meteorologists focus on dew point instead of relative humidity.
We actually had two weather stories unfolding. While the Twin Cities climbed to a scorching 100 degrees during the afternoon, the other impressive statistic may have been the dew point, which reached an astonishing 81 degrees earlier Monday morning.
Interestingly, the dew point didn't stay that high all day. As drier air mixed into the atmosphere, dew points fell significantly during the afternoon. That drop in moisture actually helped temperatures soar into the triple digits.
Had the dew point remained in the low 80s throughout the day, the atmosphere would have struggled to heat up as efficiently, likely keeping air temperatures a bit lower while sending the heat index even higher.
In other words, Minnesota traded some of its tropical humidity for even hotter air. The result was a rare combination of a 100-degree temperature and a morning dew point more commonly found along the Gulf Coast.
So while the century mark grabbed the headlines, it was the tropical-level moisture earlier in the day that made stepping outside feel like walking into a sauna. That's why meteorologists focus on dew point when talking about humidity. It tells us what the air actually feels like, not just what percentage of moisture it can hold.
The next time you wonder how humid it is, take a look at the dew point. That's the number meteorologists are watching, and it's the number that explains why some summer days feel comfortable while others feel like you're breathing through a warm, damp towel.
