What Is Humidity And How Does It Affect The Weather?

What Is Humidity heading

For most of us weather enthusiasts and many people just interested in the weather, the influence and importance of humidity on various weather systems and atmospheric conditions are very well-known.

While we pay so much attention to humidity and its influence on various weather conditions and different scenarios, we sometimes miss the simple but important question many people don't know the answer to, and sometimes we ourselves are not so sure about...

What Is Humidity


The term, humidity simply refers to the amount of water vapour present in the atmosphere at any specific time. Water vapour is nothing more than water in a state of gas (after the liquid has evaporated). Although humidity and its effects can usually be felt, it is normally invisible to the naked eye.

At any given time, no matter where we find ourselves (indoors or outdoors), we are constantly surrounded by air containing a certain percentage of humidity.

It is actually very important for air to contain just the right amount of moisture to maintain a "balanced" air ratio, to be beneficial to the environment and all living organisms. Too little or too much humidity, and it can negatively impact the environment and even human health. (More on this in a later article.)   

Humidity is also a crucial element necessary for the formation of snowflakes and hailstones in subzero temperatures, which you can read more about in this article.

Relative Humidity And Absolute Humidity

Before explaining how humidity is measured, we need to address the difference between relative humidity and absolute humidity, as there is some confusion about the difference between the two.

Absolute humidity is the measurement of the amount of water vapour in the air. It is a very rigid form as measurement, as it does not take variables like temperature into consideration. It is normally indicated as grams of moisture per cubic meter of air (g/m3).

Relative Humidity

Relative humidity is also the measurement of the amount of water vapour in the air. Unlike absolute humidity though, it is measured relative to the temperature of the air.

This is important, as warm air can hold much more water vapour than cold air.

If absolute humidity is used to measure the water vapour in both warm and cold air, and an identical water vapour percentages are measured in both, it is misleading and not representative of the actual conditions.

(In the above scenario the relative humidity in the cold air is actually much higher than that of the warm air. This is simply because, as already stated, warm air can hold more water vapour than a similar volume of cold air. This means a lot more moisture must be present in the cold air to match the moisture in the warm air to have an equal value when absolute humidity is measured.)

For this reason, relative humidity is the most widely used way of measuring as it most accurately reflects the actual conditions and "feel" of the air.  

How Humidity Is Measured

The instrument used to measure the humidity in the air, is called a hygrometer. There are a variety of these instruments that have been used through the years.

The psychrometer is probably the most well-known early example of a humidity measuring device. It basically consists of two thermometers (one being covered with a wet cloth), used to measure the humidity.

The bulb of the thermometer covered by the wet cloth measures a lower temperature as a result of the evaporation of the moisture in the cloth.  Using the difference between the two different temperature readings. the humidity is measured.

Obviously, this is not a very accurate and reliable way of measuring humidity.


A capacitive or resistance hygrometer uses a much more reliable way to measure humidity. A material able to absorb moisture is used. The amount of moisture influence the material's ability to carry an electrical current. 

An electrical current is then sent through the material and measured. Based on the strength of the current (influenced by the amount of moisture absorbed by the material), the amount of humidity in the air can be measured.

The process clearly is a bit more complex than just explained. To get a better understanding of hygrometers and how they measure humidity, you can read more about it in this article.

The Effect Of Humidity On The Weather

Humidity is one of the main driving forces of almost weather system around the world. Actually, the combination of humidity and temperature are the impetus of many weather systems and occurrences.

The moist air in a warm front gently moves over a cold front and cools down as it rises. It results in condensation and cloud formation, which leads to the gentle precipitation that is welcoming to the agricultural sector. (Similar to the weather produced by a stationary front.)

On the other side of the scale, the warm moist air over the oceans of the tropics rise and form powerful low-pressure systems. As the air keeps rising and rotating winds are pulled in and building up around the low-pressure centre, the warm humid air keeps feeding the growing system.

hurricane, cyclone and typhoon

What was a tropical depression, can now quickly build into a tropical storm. If enough humid air builds up in this system and it stays over the warm ocean waters long enough, hurricanes of varying strength can form that can be very destructive when it makes landfall.

And this whole process got started by some humid air rising up from the ocean's surface. That is why these warm tropical waters are called the engine rooms of big storm systems, and the fuel that drives these massive systems.

Similarly, the torrential rains falling during the Monsoon Season over India and Southeast Asia is al part of the circulation pattern that brings huge amounts of humid air from the warm Indian and Western Pacific Oceans during the warm summer season.

As is the case with hurricanes and tropical storms, moisture-filled air is once again one of the main driving forces of a major weather system. This is also another example of how humidity and temperature work together in the creation of a major storm system.

There are obviously many more processes involved in the formation of all these weather systems. If you want to read in detail how hurricanes and monsoons are formed, as well as the role humidity plays in all this, you can read the in-depth article here.


The meaning of humidity, in other words, what exactly it is, should now be very clear. You also now know how it is formed. It may not always be always visible, but its power and influence can never be underestimated.

The powerful effect it has on the weather on a global scale should also be very evident, and we have just touched the surface.

There is actually so much more to humidity than I covered in this post, but as long as you now have a clear understanding of what exactly humidity is and how it is formed, this article served its purpose.

Feel free to leave me any comments, questions or suggestions, and I will get back to you as soon as possible.

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Until next time, keep your eye on the weather!


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The Difference Between Weather And Climate - And How It Influence Us. - March 6, 2019

[…] If you are unfamiliar with humidity and the role it plays in weather and climate, you can find all the information in this article.  […]


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