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Opinion: It's Just the Dewpoint Dummy

Andrew Freedman @ 8:06 AM

Andrew Freedman rejoins to write a regular Sunday opinion column.

While you were paying attention to arguably more important events in the Middle East and on the terrorism front in early August, Houston television station KPRC eliminated the dewpoint from its weather forecasts after determining that viewers don't care about it and don't understand it. Firing the dewpoint points to a possible large scale failure of TV weathercasters to educate viewers about basic elements of meteorology and how the science relates to their daily lives. It also makes me fear for what comes next. No data is safe anymore. Yes, wind speed, I'm looking at you. And don't smile over there, last night's low temperature. You're not looking so good either.

Jason Samenow's Sunday Forecast

Nice Day StampBeautiful. It's going to be another day of low humidity, and full sunshine. With all the sun, temperatures will warm into the mid 80s -- it will feel more refreshing in the shade, or in the water. Overnight, clear skies, with a low near 60 in the suburbs, mid 60s downtown.

Check back tomorrow for the complete week ahead forecast.

Houston Chronicle columnist Ken Hoffman hailed the move in an Aug. 7 column as "the greatest breakthrough in weather forecasting in the past 50 years."

He said KPRC Chief Meteorologist Frank Billingsley told him during a bowling tournament (yes, you read that correctly) that station research shows the dewpoint just doesn't rank high on the list of what viewers want to see on their weathercast, so the station decided to stick to relative humidity instead (which is an entirely different measurement, and is about as useful as the NOGAPS computer model).

"I don't know what the dewpoint means. How it's calculated. Why it's important. Or how it affects anything in anybody's life," Hoffman wrote. "The dewpoint is absolutely worthless information."

The saddest part about the dewpoint getting the pink slip is that KPRC's Billingsley couldn't even explain it properly. Hoffman quotes the TV weatherman as saying to him during the bowling tournament (yes, I thought I'd mention that again), "Air has to cool to a certain temperature to produce moisture. The dewpoint is that temperature, but it changes as does the actual temperature, so it's confusing."

Wow. And this is coming from a meteorologist whose online bio states that his passion is explaining meteorology to the public. "I try to make the weather clear and easy to understand. It's a challenge taking a complicated subject and making it simple and I really enjoy it."

For the record, according to the American Meteorological Society, dewpoint is defined as "The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur."

A slightly more readable definition from The Weather Channel's glossary defines it as: "The temperature to which air must be cooled at a constant pressure to become saturated."

Dewpoint can be more easily explained by stating that it is a measurement of the moisture content of the atmosphere, and is important for determining everything from severe weather potential to the ability of the human body to cool itself off when it becomes overheated. For example, in the recent heat wave, dewpoints in many regions of the country skyrocketed into the upper 70s, which created deadly conditions by making it nearly impossible for people to cool themselves off through the normal, if unwelcome, process of sweating. Relative humidity didn't help kill people, the dewpoint did. Relative humidity is a different measurement, but is often confused for dewpoint.

KPRC's action spurred meteorologist Matt Lanza of WKTV in Utica, New York to write a passionate defense of the dewpoint on his station's blog. In it Lanza wrote:
Dewpoint is the single most vital piece of information there is to help gauge how comfortable you will feel if you step outside in the summer.

If you step outside and it's 75 degrees with a 75 degree dewpoint... it feels flat out disgusting! But if you step outside at 55 and feels a little humid, but it's actually not too bad. Yet the humidities are exactly the same!

So how is the "relative humidity" helping you at all?
My answer: it isn't. So let's drop this misguided attempt at simplifying things for viewers and give them what they really need to know.

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