Thirsty (for knowledge) Thursday: Using "Dew Point" Instead of "Humidity" for Runners

The coach on my running team recently shared this article with us. The author urges athletes (specifically runners) to utilize dew point instead of humidity as a metric they track. He argues that it's the dew point that truly tells you how comfortable it is outside.

Humidity Can Be Deceptive

What runners interpret as high humidity isn’t always the case.

For example, 90°F (32°C) at 60% humidity will feel pretty humid outside. When the temperature is hotter, it’s not uncommon for people to say the humidity is really high even though the actual percentage is relatively moderate.

What they’re really feeling is a higher dew point. 🤯

Humidity Is Not Useful by Itself

You might see 100% humidity and think to yourself, “That stinks. It’s going to feel really muggy outside.” But that percentage alone doesn’t tell you anything useful.

For humidity to be helpful, you also need the temperature.

Consider these examples:

Both temperatures have the same humidity, but they feel drastically different.

For humidity to be useful, you need a lookup table that shows what it’ll feel like at different temperature/humidity pairs. As you’ll learn later, that’s unnecessarily complicated compared to the dew point.

The Root Reason

While I’ve been referring to relative humidity as just humidity, the two primary downsides above are because of the word “relative.”

Humidity tells you how much moisture is in the air relative to how much the air can hold. So when the humidity is at 100%, that means the air is saturated with moisture and can’t hold any more. If it’s at 50%, the moisture “glass” is half full (or half empty? 🤷🏻‍♂️).

And a critical characteristic of humidity is: The higher the temperature, the more moisture the air can hold.

This explains why Example B above feels muggier. At the same humidity, the higher temperature means there’s more moisture in the air compared to a lower temperature.

This is what makes humidity deceptive.

The relative nature of humidity is what makes it hard to interpret.

What we really want to know before heading outside is the absolute, not relative amount of moisture in the air. That’s what determines how muggy or humid the air will feel.

And that, my friend, is where the dew point swoops in and saves the day.

The Upsides of Dew Point

The dew point tells you how much moisture is in the air which easily translates into how it’ll feel outside.

Unlike humidity, dew point is an absolute measure, not relative.

A 50°F (10°C) dew point will always feel comfortable outside regardless of the temperature or humidity. Whereas a 50% humidity will feel different depending on the temperature.

This is why the dew point is so much more useful than humidity.

It’s “portable.” You just need one number. And it’s practical. No big lookup tables needed.

All you need is this table (which is easily memorized)...

Comfort Levels at Various Dew Points

Consider these examples:

Since comfort is subjective, use the table above as a starting point.

If you live somewhere more hot and humid, the 60–64°F (16–18°C) range might actually feel comfortable to you whereas someone used to cooler and drier conditions might consider it moderately uncomfortable.

The key is making note of the dew point ranges that feel comfortable and uncomfortable to you and making decisions based on those ranges.

And one disclaimer... a dew point in the comfortable range doesn’t mean performance is unaffected. Higher temps with lower dew points can affect performance just like lower temps with higher dew points.

How Do I Use Dew Point Before a Run?

With a little practice, it won’t take long before you’ll be able to tell how comfortable (or uncomfortable) a run will be from just the dew point.

Note, the following also applies when running in hotter temperatures.

Stay Cool

As the dew point gets higher and more uncomfortable, it’s much harder for the body to cool itself. A higher dew point means more moisture in the air which makes it harder for sweat to evaporate and create a cooling effect.

So here are some other ways to help with cooling with higher dew points:

- Choose a route with more shade.
- Wear technical, sweat-wicking clothes.
- Wear a hat soaked in cold water.
- Drink more water or sports drink per hour.
- Adjust power/pace targets based on the weather.

The last point is worth reiterating, especially for long runs or higher intensity efforts.

If the temperature or dew point is higher than your typical training conditions, you should adjust your power/pace targets accordingly.

This ensures you’re running at the correct effort.

A half marathon tempo workout isn’t training the right physiological system if it feels like a 10k effort. It’s so important to adjust targets based on the weather for these reasons:

- Your body gets the right stimulus.
- You don’t over exert yourself.
- You reduce the risk of injury (by not running harder than you should given the conditions).

The article goes on to mention a few places to get dew point info, and a few places where you can help calcuate your power or adjust your pace based on the dew point. So check out the article for more if you are interested.

For more "Thirsty Thursday" posts that highlight workouts, body science, and all kinds of interesting information, CLICK HERE. As always, check back for some "Friday Funnies" tomorrow!