It’s a bird, it’s a plane, it’s a…weather balloon?

If you follow us on Facebook, you may have noticed the the Albany National Weather Service made regional headlines last week. Why? Because a weather balloon which was launched from the office here in upstate New York made its final descent onto a driveway in Rhode Island! Thus, we thought it would be a good time to go over what exactly IS a weather balloon (and what you should do if you find one in your driveway!).

A weather balloon, or radiosonde, as they are called, is a relatively simple piece of instrumentation which has been used for many decades to take measurements of the atmosphere at locations high above the earth’s surface. Since the atmosphere is a three dimensional fluid which covers the whole globe, it is important to have measurements taken in as many locations as possible to get a ‘snapshot’ of what the state of the atmosphere is at a particular time. In the United States, the National Weather Service has been taking measurements with radiosondes since the 1930s.

Radiosonde launch, c. 1936.

The radiosonde is the small instrument package which is attached to a very large helium (or sometimes hydrogen!) balloon such that it is carried upward through the atmosphere. Sensors on the instrument package take measurements of a variety of parameters, including temperature, humidity, and wind speed and direction. The position of the balloon as it ascends is tracked by GPS, although in the ‘old days’ the radiosondes were tracked via theodolite.

Worldwide radiosonde sites. Courtesy National Weather Service.

Radiosondes are launched at least twice daily at stations around the world at the same time. Here along the east coast, they are launched during the hour prior to 8:00 AM and 8:00 PM during Daylight Time, and 7:00 AM and 7:00 PM during Standard Time. That means that dutiful civil servants and National Weather Service employees on the west coast of the U.S. are getting up to launch weather balloons three hours earlier, before 4:00 AM and 4:00 PM. By taking a three dimensional ‘snapshot’ of the atmosphere using radiosondes launched around the world at the same time (in addition to many other types of weather observations), computer forecast models can determine the ‘initial state’ of the atmosphere from which our weather forecast models are generated.

Map depicting winds at the 250 mb level (approximately the height of the jet stream) at 8:00 AM EDT on 4/13/2019. Courtesy Storm Prediction Center.

In addition to giving forecasters a good picture of where important upper-level features, such as the jet stream, are located, plots of individual radiosonde stations can be created and are an invaluable tool for forecasting severe weather and mixed winter precipitation. In the graphic below, known as a ‘Skew-T Log-P’ diagram, forecasters can use the raw radiosonde data (plotted on the graph), as well as numerous calculated parameters to evaluate the potential for development of hail, tornadoes, flash floods, and ice, among many others.

Radiosonde data and calculated parameters from Albany, New York at 8:00 AM on 5/13/2019.

So, back to the original story which prompted this post. How did a radiosonde from Albany, New York end up on a driveway in Rhode Island?

Courtesy WPRI.

Well, as the weather balloon rises through the atmosphere, the helium balloon gradually expands. Eventually, it gets large enough where the latex can no longer stretch, and the balloon pops. A parachute (the orange object in the picture above) deploys, and the instrument package gently falls back down to earth. As you might imagine, the balloons tend to drift with the winds in the upper atmosphere, and since our jet stream often blows from west to east, many balloons land to the east of the original launch site. While only a small percentage of radiosondes are actually found and returned, the National Weather Service does recycle them when possible. If you find a used radiosonde, you will see that there is a postage paid envelope and return directions included on the instrument package. You can always contact your local National Weather Service office if you have any questions.

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