The tale of humidity and the heat index

KOIN 6 Weather Kids

PORTLAND, Ore. (KOIN) – Have you ever heard that dry heat in the desert is easier to handle than a humid environment in the southeast? You may have heard “it’s not the heat, it’s the humidity that gets you.”

Well, there is a reason for this and in this lesson, we will discuss the relationship between temperature and humidity and what it means for your body.

Weekend Meteorologist Joseph Dames

Now you may think that here in Oregon and Washington, we sort of have it made. It’s not that humid and if you’re west of the Cascades, the relative humidity doesn’t get too low or high. However, there are times in the summer we have to deal with humid conditions and there are times that we lean to dry conditions. This summer, we’ve actually had some moments where it was not only hot, but we had heat indices that were 5 to 10 degrees higher than our high temperature.

Wait…what are heat indices? Continue below!

Heat Index (HI) – This is an index that takes air temperature and relative humidity and combines them through a formula to determine an apparent temperature. This is a good way to display how hot it actually feels. Heat indices are the digits that represent that apparent temperature.

The National Weather Service (NWS) in Portland has a twitter thread from August that discusses this exact situation around Portland and Eugene. If you have an account, you should check that out too.


What exactly is going on and why do we use these parameters to help determine this index? Humidity plays a large role in the ability to cool down. You see, when we become hot, we tend to sweat. We perspire to help cool down with the art of evaporative cooling. Essentially, the sweat from our body helps remove the heat near our skin as it evaporates.

However, when the air is humid, this process is much harder to accomplish. If the relative humidity is high, you can assume that there is a decent amount of moisture already in the air. If that is the case, then that moisture on your skin doesn’t have anywhere to go! Have you ever had a hard time drying a wet towel even though you have it outside? This is a similar process. That is why dry heat is more manageable compared to a humid environment because when you sweat it can go through the cooling process of evaporation.

Interested more on how humidity may impact your style, check out this article from Chief Meteorologist Natasha Stenbock.

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