One of our most critical programs at the National Weather Service in Nashville is the upper air program. Upper air observations have been taken at Nashville since the 1940s and at our current location since July 1963. Nashville is one of 92 National Weather Service stations and one of nearly 900 stations in the world that launches weather balloons twice each day. The data collected by the weather balloons are ingested into computer forecast models where equations are run using the data. The end result is a computer model forecast that enables the human forecaster to ultimately determine whether or not the output seems meteorologically reasonable. Therefore, the vital data collected by the weather balloons give forecasters guidance to produce a forecast for short-term (up to 48 hours) and long-term periods (up to seven days).
NWS Nashville upper air building, July 1963. Photo courtesy of Bobby Boyd.
Each station around the world launches the balloons at the same time to provide a snapshot of the three-dimensional state of the atmosphere. At Nashville the balloons are launched at 6:00 AM and 6:00 PM during daylight saving time and 5:00 AM and 5:00 PM during standard time. Occasionally, special balloon launches may be requested, particularly if severe weather is expected. Another interesting scenario occurs when a tropical cyclone poses a threat to the United States coast. 6-hourly special launches may be needed from select upper air stations in order to allow forecasters at the National Hurricane Center to more accurately forecast where a tropical cyclone may move. In fact, all of the upper air stations in the continental U.S. launched special flights every six hours for a few days as Hurricane Sandy approached the East Coast in October 2012. All of this data was ingested into computer models and allowed forecasters at the NHC to produce precise track forecasts with a high degree of confidence.
This tour will give you a detailed look at how meteorologists at the NWS in Nashville take upper air observations. If you want to skip all of the images and text, you can watch a short video of an actual balloon launch below!
The tour will begin at the upper air inflation shelter building, which is just a short walk up a hill outside of our office. The building has a few different areas, including the white dome at the top of the building that houses a lot of the upper air hardware, the small side room that houses the hydrogen tanks, and the main room where the balloon is inflated.
Inside the white dome at the top of the inflation shelter is where the Telemetry Receiving System (TRS) is housed. This is basically the guts of the upper air system. The dish below collects the signal transmitted by a radiosonde and transmits it to the computer system inside the office for processing. This system is called the Signal Processing System (SPS).
The small room on the right side of the building is adjacent to the main room and is where the hydrogen tanks are stored. We have to take extra precautions not to create any static charges since hydrogen is a flammable gas. Each tank of hydrogen can typically fill up two and a half to three balloons.
The main room is where the balloon is inflated and where the flight train is prepared. There are two garage doors attached to this room that allow us to launch from either side of the building, depending on the wind direction. This may not seem like a big deal, but it is a tremendous advantage when the winds are strong. Another thing to note is that this building has no insulation. Therefore, we must dress for the elements, particularly in the winter!
Before we begin with the process, we will gather the supplies needed to take an upper air observation. In the clear bag is the radiosonde, then a parachute, and a latex balloon in the black bag. All three of these will eventually be tied together and launched.
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