How weather balloons work and why they’re crucial to forecasting

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CHATHAM, Mass. (WPRI) — On a beautiful evening at the Monomoy National Wildlife Refuge on Cape Cod, Tim Morrissette, the lead upper air observer for the National Weather Service, releases a balloon from his hand that rises and quickly appears as a speck over the horizon of the Atlantic Ocean.

As it journeys into the upper layer layers of the atmosphere, the balloon begins to record data that’s critical for forecasting weather, especially during severe weather.

“It’s measuring directly temperature, calculating the dew point temperature, and also pressure,” said Alan Dunham from the National Weather Service’s Taunton office.

The balloon is launched twice a day, once in the morning and once in the evening, at sites all over the world including Albany and Brookhaven in New York and Grey, Maine.

However, Dunham said that Chatham is the furthest east upper air site in the continental United States.

Before the balloon takes flight, there is a lot of work that needs to be done.

Morrissette attaches the balloon to a hose that slowly inflates it with helium. He then walks to a trailer next door and sets up weather instrumentation and software that will gather data from the balloon.

The actual device that will be on the balloon and recording the weather data is called a radiosonde; it’s surprisingly small and simple. It has a sensor for temperature, humidity, pressure and also has a GPS unit that calculates wind speed and direction.

Next, Morrissette heads back to the garage and attaches a rope and parachute to the radiosonde. He is careful to make sure the rope is the correct length for the wind speeds that day.

The balloon can exceed elevations of 100,000 feet. It eventually bursts and the radiosonde and parachute usually end up landing in the ocean, but occasionally they drop back on land.

A balloon launched in Albany did just that several years ago, according to Dunham.

“We got a call once from a very concerned lady,” he recalled. “There was this package in a tree with a parachute and she was convinced it was a bomb.”

So why are these balloon launches so important? The computer models that the Pinpoint Weather Team uses depend on the data they collect.

The launches have to be done correctly and consistently, or else the accuracy of the forecast can suffer.

“There is an old saying with computers: garbage in, garbage out. Same thing with the weather forecast models,” Dunham added. “If you have lousy information going into the model, you are going to get a lousy forecast out of it.”

Click here to look at data collected from weather balloons »