“Whew! What’s the humidity today?”
That’s a question I get a lot in the summer. And what people are really asking for is the “relative humidity” value. Relative humidity is a measure of humidity that most meteorologists hate and one you don’t see in our weather reports very often. Why, you ask?
Relative humidity is like a cup of Starbucks coffee. While the fine baristas at Starbucks will fill your cup to the top, a cup of “venti” will hold more coffee than a “grande” and a “grande” will hold more than a “short.”
Humidity is the same. The temperature outside determines the size of your cup. When it’s cold outside, the air will only “hold” a small amount of moisture. So we can have 100% relative humidity in the winter and still be bone dry. That’s why in the winter you have to deal with chapped lips and static electricity.
The warmer it gets, the larger the “cup” gets. That’s why we don’t think relative humidity is a very good measure of humidity.
Meteorologists generally prefer to use the dew point temperature to measure humidity. The dew point is the temperature at which the water vapor in the air will begin to condense into liquid water. Basically, the air can no longer “hold” more water. The dew point will never be higher than the air temperature.
Dew point temperatures below 50 mean there’s not much moisture in the atmosphere. For most people, dew points between 50 and 60 are ideal. This week, we’re seeing dew points in the low-to-mid 60s, which is slightly humid. But over the next few months, we’ll likely see those dew points climb into the 70s as the hazy, hot and humid days of summer settle in. Perfect iced coffee weather!