The weather data and forecasts you obtain from television news, the Internet, or a flight service station are products of an elaborate enterprise that includes the National Weather Service, other federal agencies, and private companies such as Lockheed Martin, which the FAA contracted in 2005 to take over the operation of flight service stations.
When you're getting ready for a flight you need to obtain two kinds of weather information: Observations of what the weather is doing now and forecasts of what it will do in the future. How much information you need depends on your plans. On a day when you're going to stay in the traffic pattern at your home airport and the weather looks fine, you should still check the forecast to see if any weather trouble is expected to show up while you'll be in the air.
If all you knew about the current weather was what you could see from the ground, and if you knew a fair amount of practical meteorology, you might make a pretty good forecast for thunderstorms an hour or two from now, if the visibility was good enough to see the tops of cumulonimbus (thunderstorm) clouds a few miles away and winds aloft--as shown by other clouds moving overhead--were coming from the direction of the thunderstorms.
Figure 1 (top) is an analysis of the weather at a given time. The surface chart shown in Figure 2 is a forecast of pressure patterns, fronts, and precipitation. |
Still, you shouldn't count on seeing thunderstorms that could arrive in an hour. Even if you're flying around and around the pattern, you should land before thunderstorms loom on the horizon because winds blowing down from a thunderstorm could hit the airport with gusts that quickly change direction as well as speed. And you would not come close to predicting what kind of weather you would encounter during a 100-mile flight even when the weather at your location is fine.
All of the weather information you receive, whether from television, the Internet, or a formal preflight briefing, is either observations of what the weather is doing now or forecasts of what it is likely to do. If the observations are plotted on a map, like the one from the NWS in Figure 1 that gives a snapshot of the weather at a certain time, it's called an analysis. A map showing a forecast is called a prog for prognosis.
The system we use now for obtaining both observations and forecasts began in the middle of the nineteenth century with that era's growing knowledge of how the weather works--and the invention of the telegraph.
The telegraph enabled forecasters to learn, in real time, what the weather was doing all over a large area, such as the United States. Using data telegraphed from around the country, meteorologists drew weather maps showing patterns of high and low surface air pressure, winds, temperatures, and precipitation across the country at particular times. Using these maps and a few simple rules, such as most storms affecting the United States except hurricanes move very generally west to east, enabled them sometimes to make fairly good predictions. But these forecasters also had some notable failures.
The keys to producing good weather forecasts that meet today's needs are:
The forecasts that you need before taking off to fly over the horizon are much, much better than any available even a decade ago. The credit goes to technological advances, including improved weather data collection systems, increasing knowledge of how the atmosphere works, and the constantly growing power and speed of computers.
In the United States, most surface data comes from automated instruments that measure temperature, humidity, air pressure, precipitation amounts and types, and wind speed and direction. The National Weather Service's automated surface observation system is an example. When these systems are at airports they also measure and report visibility and the heights above ground of cloud bases.
Upper-air data comes from weather balloons, launched twice a day around the world to measure temperature, air pressure, and wind speeds and directions from the ground to higher than 50,000 feet, plus humidity at lower altitudes, and radio the data back to weather offices. Automated reports from many airliners add more upper-air wind and temperature data. Pilot reports from you and other general aviation and airline pilots help fill gaps in this data stream.
Weather radar images are a mainstay of television meteorologists because they can show viewers in real time what a thunderstorm or snowstorm is doing. Weather radar is also useful to pilots--when they can obtain the information. But pilots need to know that in general, air traffic controllers don't have direct access to the kind of weather radar images you see on television. You can't count on a controller to be able to safely steer you around dangerous weather.
Today's forecasts begin with global surface and aloft weather data being fed into computers at the National Weather Service's National Centers for Environmental Prediction headquartered in Camp Springs, Maryland. (Other nations have similar centers to produce their forecasts.) The supercomputers there use various kinds of models to produce maps and text forecasting the weather at different times in the future.
These forecast maps and text are sent to National Weather Service local offices around the nation; to NWS specialized offices such as the Aviation Weather Center in Kansas City, Missouri; flight service stations; online services, including FAA Direct User Access Terminal service providers CSC and DTC; private companies, including television stations or companies that provide forecast to television stations; and others.
Figure 2 is an example of a product from a private forecasting firm: Meteorlogix, a large weather firm that produces forecasts and other weather-related products for a variety of customers. It's a forecast map called a surface chart, for 12 hours after the time of the forecast that shows atmospheric pressure patterns, fronts, and locations of precipitation forecast for its "valid time." Such a surface prog chart is only the beginning of the products you should consult before embarking on a flight away from your home airport. The text forecasts you should consult include:
Your local television meteorologist is a good source of information about the general weather picture, including such things as whether driving out to the airport will be worth your time tomorrow. And nothing beats a good local television weather broadcast when you're at home and severe thunderstorms or tornadoes threaten your area.
But to ensure that severe thunderstorms or other dangerous weather will not threaten your flight, you need to turn to the system that combines government agencies, such as the NWS, and private companies to gather weather data, produce forecasts, and make them available to those who need them--including pilots.
Jack Williams is coordinator of public outreach for the American Meteorological Society. An instrument-rated private pilot, he is the author of The USA Today Weather Book and The Complete Idiot's Guide to the Arctic and Antarctic, and co-author with Bob Sheets of Hurricane Watch: Forecasting the Deadliest Storms on Earth.