Dew Point refers to the saturation of water in the air, or more simply the level of humidity you'll feel when you step outside. On this page, we will review critical factors that will help you prepare for the weather based on the forecast. You'll find out the difference between relative humidity and dew point along with some handy illustrations. Plus, get an idea of what different dew point degrees actually feel like. If your weather station doesn’t provide you with the day’s dew point, you can use our calculator to figure it out - just add the temperature and relative humidity to get the dew point.
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Your weather forecast
Depending on where you are in the world, you can experience a significant variance in weather patterns. Some regions get humid for a few weeks out of the year while other places can have extreme rain and moisture for months on end. Like most people, the things you do could be influenced by the weather.
There’s nothing worse than preparing for a hot day only to be greeted with a cool breeze. It looks like you needed that light jacket after all, and your plans to go to the beach will have to wait. This type of scenario is more likely when you are on vacation and not too familiar with the climate of the region.
So what went wrong? Chances are, when you checked the weather forecast, you noticed a high percentage of relative humidity. Relative humidity can tell you a lot about the moisture in the atmosphere but isn’t useful for the average person trying to plan their day or weekend.
When checking the weather, it’s important to consider some other factors. Air temperature can help quantify the relative humidity in the forecast. Alternatively, paying attention to the dew point is a great way to prepare for the day. If your outlook doesn’t give you the dew point, you can quickly figure it out using the air temperature and relative humidity.
What air temperature tells you
To appreciate relative humidity, it’s essential first to understand how air molecules act
at different temperatures
. Air molecules are held together differently when the air temperature is hot or cold.
When it’s cold, air molecules are pushed together very tightly. That means there is very little room for water vapor between the particles at
more frigid temperatures
. Conversely, hot air molecules are spread far apart. When there is more
heat in the air
, there is a higher potential for water vapor to fill the spaces between the particles.
Since the density of air molecules changes based on the temperature, that means relative humidity will vary based on temperature too.
What is relative humidity?
Relative humidity describes how much vapor is present in the air, relative to the air’s potential for moisture. When the relative humidity is 100%, it means the air is packed with moisture. If there is only 25% relative humidity, the air only has a quarter of its possible vapor. However, by itself, relative humidity doesn’t directly indicate how much moisture is actually in the atmosphere.
Since cold and hot air molecules are spread out differently, relative humidity can mean many different things. A cold day with 100% relative humidity is comparable to a full, 6oz glass of water. Meanwhile, a hot day with 50% relative humidity is like a swimming pool that’s half full.
When you compare the two, the half-full swimming pool contains more water than the full 6oz glass, even though it’s the lower percentage of relative humidity. That’s because there is a lot more potential for moisture in the hot air. So to truly understand what the relative humidity in the forecast means, you have to pay attention to the air temperature as well.
By observing these two aspects of the weather, you can then figure out the dew point. Dew point is a more accurate measure of what you will feel when you step outside. When talking about whether a particular day will feel “muggy” or “damp”, the dew point is a more accurate term to use.
Dewpoint and comfort
Dew point is an absolute measure of the moisture in the atmosphere. It can tell you how many grams of water are in each kilogram of pure air. Even though relative humidity and dew point give you an idea of the atmospheric moisture; only dew point is an accurate measure of the vapor that is present in the air.
Dewpoint measurements can reach from zero to one hundred. Most people are comfortable at a dew point of around 50 to 60 degrees. At that dew point, you could expect a pleasant day without too much humidity. As the dew point get’s higher, it means there is more vapor in the atmosphere. For example, a dew point measurement of 70 degrees will feel quite sticky. See the figure below for an idea of what you will feel at different dew points.
Next time you are planning your weekend, use this simple humidity measurement. If your forecast doesn’t give you the dew point, just add the temperature and relative humidity to the calculator.
Remember to bookmark this page and save it to the home screen of your smartphone. Keeping this great tool at your fingertips can be useful when you’re on vacation or if you have guests coming from out of town. This way, the weather will never catch you off guard. If you found this page useful, you can promote us on social media by using the share feature.