Sometimes decoding the weather forecast is more than just the highs and lows, especially when it comes to humidity.

Buzzy weather words like dew point or relative humidity often leave forecast lay people high and dry when it comes to actually knowing what to wear.

So stay tuned for our special report on how to make sense of the chemistry behind muggy weather.

Humidity is a measure of how much water is dissolved into the air.

It's a pretty straightforward concept.

Where it gets tricky is that there's an upper limit to the amount of water that can be dissolved in the air.

That changes based on the temperature.

The hotter the air, the more water can be dissolved in it.

So for example if the temperature is 41 degrees Fahrenheit, you can dissolve up to five grams of water into a kilogram of air.

But if the temperature is 77 degrees you can dissolve up to 20 grams.

When it comes to back sweat you would assume that 20 grams per kilogram is going to feel much much stickier than 5 grams per kilogram, but it might surprise you to know that your local weather forecast would report these two examples of humidity as the exact same: 100%.

When you see this percentage of humidity on the local forecast, the meteorologist is referring to something called relative humidity.

This is a measure of how much water is dissolved in the air divided by how much water could be dissolved in it at a specific temperature.

In other words, relative humidity shows how close the air is to full saturation.

85 percent relative humidity means the air is 85 percent saturated.

Both of our examples are at a hundred percent saturation, or a hundred percent relative humidity.

So why is it that the second example would feel so much more sticky?

Because of how your body cools itself with sweat.

Sweat cools your body down because water molecules in it absorb thermal energy from your skin, evaporate, and take some of the heat energy with them.

If the air is at a hundred percent relative humidity there's literally nowhere for that sweat to evaporate off to so it stays stuck dripping down your lower back or in your armpits.

At lower temperatures your body won't produce as much sweat, so it's less of a problem.

If you live in a place with consistent year-round temperatures, you can rely on relative humidity to inform your wardrobe choices, but anywhere else -- and we cannot all be so blessed as to live in San Diego -- it alone isn't going to give you the info you need to be prepared for the day.

This is why meteorologists also use heat index and dew point to clue us in.

Heat index supposedly tells you how hot it feels with any given temperature and humidity.

So, for example, if it's 92 degrees Fahrenheit with a relative humidity of 85 percent, the heat index is a hundred and twenty six degrees Fahrenheit, and the National Weather Service would tell you that heatstroke is likely, so stay inside.

This can be useful, but how it feels is pretty subjective.

Dew point, on the other hand, is objective.

It's the temperature that the air needs to be cooled to to reach 100% relative humidity.

You can imagine that if the dew point is high, it's going to be a pretty muggy day.

To understand how it works, take a look at this little box here.

Let's say that inside the box it's 55 degrees Fahrenheit with the relative humidity of 90%.

At this temperature, the air is capable of having more water dissolved in it than is physically inside of the box.

If we lower the temperature slightly to 52 degrees Fahrenheit, the upper limit of the air decreases slightly to an amount equal to that of the water trapped inside of the box.

This means that we've reached 100% relative humidity.

This 52 degrees sweet spot represents the dew point.

If you get colder than the dew point, the air would be unable to dissolve all the water and condensation or dew would begin forming inside.

That means the dew point can't be higher than the temperature of the air because when the two temperatures meet dew starts to form.

To stay crisp, we want to stay away from high relative humidity.

So keeping an eye on dew point helps you know the temperature to look out for.

You can use this to your advantage when watching the weather.

As a general rule, most people will feel comfy and crisp if the dew point is below 60 regardless of the temperature.

Dew points in the 70s often feel sticky and gross.

Pro tip: the best way to work with dew points is to keep an eye on them in the forecast and then see how you feel outside.

You'll develop a sense of your favorite dew point range -- as nerdy as it is to have a favorite dew point range -- and then you can start completely ignoring relative humidity.

You're welcome.

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