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EACHUS: what happened to the relative humidity?

1 year 2 months 3 weeks ago August 05, 2015 Aug 5, 2015 Wednesday, August 05 2015 August 05, 2015 2:49 PM in Weather
Source: WBRZ Weather

On Wednesday, a viewer emailed the WBRZ Weather Team with a good, common question. Jim wanted to know why meteorologists don't talk about the relative humidity as much any more. Figuring many have the same question, our response in its entirety follows:

"Relative humidity has become somewhat of an outdated term because it doesn’t adequately convey the information it was originally intended to do.

You see, the relative humidity is a percentage that indicates “how saturated the air is with moisture.” Precisely, the number is calculated dividing the vapor pressure by the saturation vapor pressure—two terms that mean absolutely nothing to most people. Simply put, it is the amount of moisture in the air compared to the amount of moisture the air can hold.

So for instance, as I type this, there is a relative humidity of 46%. There are also many times in the cool season when the air temperature is around 40° or 50° and it is raining as the air is holding all of the moisture than it possibly can and relative humidity is at 100%. That communicates a very confusing message because you and I both know which of the two days is more humid feeling!

Therefore, the American Meteorological Society has worked with academic institutions to migrate meteorology education away from communicating humidity via the “relative humidity” and more towards the “dew point.” With the dew point, we have a distinct, unchanging scale with which we can measure the moisture content in the air. No matter the time of year, we always know that a dew point below 60° isn’t bad, upper 60s bring noticeable humidity and dew points in the 70s make you sweat immediately.

Any time we discuss the dew points on our weathercasts, a scale is included on the screen along with an explanation of what it means.

For those that prefer doing the math and figuring the relative humidity, it is still displayed on ALL of our newscasts. We show the current conditions graphic containing relative humidity in ALL of our newscasts. It can also be seen 24/7 on the cable weather channel."

If you've ever got a question about something we say, show or just why the weather is the way it is, feel free to contact us, your question could just end up on dot com!

Facebook: Meteorologist Josh Eachus

Twitter: @Josh_Eachus


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