Most assume relative humidity to be a good indicator of mugginess or dryness, but in reality the dew point gives a lot more information regarding outdoor conditions.

In its simplest form, dew point is the temperature at which dew forms, but it also tells you how much moisture is present in the atmosphere.

A dew point near 70 degrees means it feels muggy outside, while a low dew point of 20 indicates very dry conditions.

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Relative humidity on the other hand is a little more tricky, as it only indicates how close the air is to becoming fully saturated with moisture, which makes it dependent on the temperature as well as the dew point.

In other words meteorologists cannot calculate relative humidity without knowing the temperature and dew point first.

So suppose you watch KTVH news at 6pm in the summer and the temperature in Helena is 90 degrees, the dew point is 50, and relative humidity is 26 percent.

Then during the 10pm show you notice the temperature is now 65 degrees, dew point 46, and the relative humidity is 50 percent.

Even though the relative humidity increased over this time, the air outside is actually less humid since the dew point has dropped.

So in the future, before you assume it’s humid, check the dew point instead of solely relying on relative humidity.


And now you’re a little bit more Weather Wise.


Reporter: Mikenzie Frost