Sunday, August 9, 2009

What Is Dew Point??


Dew point, and how it relates to your comfort




A lot of times on the newscasts, we refer to the dew point. It can be a confusing number, but there are some aspects of it that will be beneficial to you, especially in the summer.

The dew point is the temperature at which the current air will saturate. This number goes up and down depending upon the air mass. But unlike relative humidity, it is a more reliable number.

Relative humidity is the humidity value of the air, relative to the current temperature. You know that 100% relative humidity in the middle of summer feels totally different than 100% humidity in the winter. Both values are accurate in their situation. In the winter, the cold air won’t hold as much moisture….so, 100% humidity then means the cold air is saturated.

But, in summer, the warm/hot air can hold a lot of moisture…so the 100% humidity value for that temperature can be extremely uncomfortable.

Here is a guide to know what dew point means in the summer:

Values in the 50s:

Very comfortable. If the air temperature is pretty warm, say in the upper 80s, but the dew points are in the 50s, you won’t notice any muggy feel in the air at all.

Dew point around 60:

This is when you start to notice the air isn’t as comfortable anymore. It isn’t muggy, but this is the level when most people start to notice a little jump out of the true comfort zone. People with respiratory ailments will start to notice this jump, and may find breathing a little more difficult than normal.

Dew point around 65:

At this point, the air is starting to get pretty humid. With dew points in the mid/upper 60s, our bodies start reacting to it. It takes longer to cool off, since the humid air won’t allow sweat to evaporate off your body easily. Think about it like this: if you hang a wet towel up in a steamy bathroom, or you paint a room when it’s really muggy, it takes a long time for that object to dry out. Also, for people with respiratory problems, higher dew points like these start making breathing more difficult, and create the need for using oxygen.

Dew point around 70:

This is the level when most people start using words like muggy, tropical, sultry, etc.
This is how it feels along the Gulf Coast and areas like Houston in mid-summer. When combined with hot temperatures, dewpoints in the 70s create high heat index values, and contribute to heat exhaustion or heat stroke for those exposed to the heat and humidity.

Dew point around 80:

Not commonly achieved in the US, but dew points of 80 are akin to a rain forest climate. We occasionally see dew points this high in the southern USA during extreme situations in the summer. In our part of the world, some mid/upper 70s dew points do occur at times during the summer, but are more exceptions versus typical.

A shorter and quicker guide:

Below 60 - nice. Around 60 - a little humid. Around 70 - very muggy.