Winds Aloft & Weather Balloons

Air masses are always on the move; changing direction and speed as they swirl around the globe. The movement of air across the earth’s surface is what we usually call wind.

Wind and temperature data from all levels of the atmosphere are necessary to create accurate forecast models. Meteorologists use model data to create the Winds and Temperatures Aloft Forecast. Pilots and dispatchers use the forecast to make accurate flight plans that optimize speed and fuel economy.

Scientists have made atmospheric observations for centuries. The first attempts at making upper-atmosphere measurements took place in the 1700s.

1930s Winds Aloft Reporting

As more airplanes took to the skies in the 1930s, accurate upper air data became a priority. In 1937, the US Weather Bureau (now the National Weather Service) created a network of stations that launched balloons with crude transmitters (radiosondes) to help meteorologists create winds aloft models. The work was tedious. Meteorologists collected and assembled the data by hand.

Today’s Atmospheric Data Collection

The old radiosonde network remains active. The NWS now launches balloons from 92 location across the US and its territories. Worldwide, over 900 stations launch radiosondes twice a day. During unusual or severe weather, stations often make additional launches. That’s a lot of weather balloons!

• 

• 

• 

Most launch stations fill the balloons with hydrogen (helium is expensive and in short supply). Radiosondes are lightweight packages that transmit pressure, temperature, humidity, and GPS position.

Weather service personnel launch balloons at least twice a day, at 0000z and 1200z (Coordinated Universal Time). A radiosonde transmits data every second as it ascends at 1000 feet/minute. After climbing to altitudes as high as 115,000 feet, the balloon bursts and the radiosonde package descends safely with a small parachute.

Watch a Balloon Launch!

The video was shot September 13, 2012, as Meteorology students from Mississippi State University fill and launch a weather balloon near Starkville. NWS Memphis representatives were in attendance to watch.

MSU has a Severe Weather Launch program that allows students to launch radiosondes on severe weather days to provide supplemental data to the NOAA/National Weather Service Storm Prediction Center.

Things to watch for:

• The guy handling the balloon makes a considerable effort not to touch the latex. Oils from human skin will cause the balloon to burst prematurely.
• After release, the team confirms they are receiving radiosonde data. The antenna and receiver can be seen next to the laptop.

How is radiosonde data used?

Researchers and meteorologists use balloon soundings for :

• Weather prediction models
• Local severe storm forecasting
• Aviation, fire weather, and marine forecasts
• Weather and climate change research
• Input for air pollution models

The Winds and Temps Aloft Forecast

Forecasters generate the aviation Winds and Temperatures Aloft Forecast using models made with the help of balloon radiosonde data. The forecast is issued four times a day and includes data that is valid for 6, 12, and 24 hours. Wind and temperature data are included for altitudes of 3, 6, 9, 12, 18, 24, 30, 34, and 39 thousand feet.

The US National Weather Service Aviation Weather Center provides the forecast in several formats. The most basic product is a tabular list of locations with wind direction, speed, and temperature at the different altitudes. The format is perfect if you’re curious about the winds and temperatures for a few locations.

Before computers, internet, and remote terminals, pilots would telephone a Flight Service Station to receive winds and temperatures aloft. The briefer would read the data for each station along the route of flight. The pilot calculated headings and ground speeds by hand. [Narrator: “It was not a pleasant task.”]

Winds Aloft Visualizations

A picture is worth 1000 words. A quick glance at tabular data doesn’t provide a “big picture” of what’s going on in the atmosphere; especially for a long route.

Wind Barbs

Sailors and meteorologists came up with an easy way to visualize winds. Weather services standardized wind symbols in the 1940s, but the concept hasn’t changed since the 1800s.

In the early days, forecasters drew the “wind barbs” on weather maps by hand. Now, the data is pulled from servers and automatically depicted. A quick glance at the screenshot below gives you an idea of forecast air mass movement and speed at 34,000 feet.

Think of wind barbs like an arrow with a point and feathers. The pointy end points the direction of the air mass flow. The feathers, or barbs, depict the wind speed. Winds aloft charts often display the temperature (in Celsius) next to each barb. Wind speed is easy to decipher…

• Short barbs = 5 knots
• Long barbs = 10 knots
• Pennants = 50 knots

Flight Planning Software

Global weather providers, including the National Weather Service, provide winds aloft data in machine readable formats. Airlines and general aviation pilots use flight planning software that can use the wind data to generate very accurate flight plans optimized for speed and/or fuel savings.

Jeppesen FliteDeck Pro X, a popular app with airlines, can display winds aloft barbs with the route of flight. This feature helps flight crews understand why dispatchers may have created a route that seems out-of-the way. The wind barbs also help pilots anticipate wind shifts and turbulence along the route.

Check out the two routes from Louisville to Anchorage in the following image. The straight line indicates the great circle route (shortest distance) and is 2713 nautical miles.

Our dispatcher generated a route that took us farther north, adding 114 nm to the journey. The longer route avoided a 140 knot headwind saving us considerable time and fuel.

Check out the low pressure area in the center of the screen shot below. The wind barbs clearly depict the counter-clockwise movement of the air mass. The “feathers” of the wind barbs always point inward toward the center of the low pressure area.

Windy Animation

Wind barbs are nice, but Windy.com improves the concept. Windy uses the machine readable model data to provide a stunning animation of air mass movement.

Windy allows the user to zoom to any area of the earth and select altitude, forecast time, and forecast model. The video below is centered on the same low pressure area as the image above. You can really see the counter-clockwise circulation.

I use Windy.com as part of my weather review before every long flight.

More About Winds

If you’d like to read more about the effect of winds on aircraft, check out Headwinds and Tailwinds.