Until you took up flying, you probably found the weather information you needed by looking out of the window and watching the weather segment of the local television news. Maybe you've moved beyond television by checking your smartphone for what meteorologists call a “tombstone forecast”—it’s brief enough to fit on a tombstone. For example: “Rain, high 51, low 34.”
Until you started flying, this was all the weather information you needed most of the time. As a pilot, you need a lot more weather information, and you’ll need it for every flight. You wouldn’t want to take off for an hour practicing takeoffs and landings unless you’re sure a line of thunderstorms isn’t lurking over the horizon to send fast, shifting winds across the runway just as you’re touching down.
Fortunately, since the 1930s, the National Weather Service (NWS) and the FAA have developed an aviation weather infrastructure that obtains weather data, produces forecasts, and makes needed information available to pilots. In the past two decades private weather companies have become key players in the aviation weather enterprise. You need to understand what kind of information is available to you and how to use it.
THE TWO FLAVORS OF WEATHER DATA. All of the weather information you obtain for a flight is either a report of what the weather was doing at a particular time in the near past, or a prediction of what it will do in the near future. All weather forecasts begin with meteorologists collecting current weather data, beginning with the regular surface reports from automated weather instruments at airports and other locations. These include temperatures, atmospheric pressures, humidity, wind speeds and direction, visibility, what kind of precipitation—if any—is falling, and the ceiling, which is the height above the ground of the lowest clouds that cover at least five-eighths of the sky.
Weather satellite and weather radar images also supply information on current weather. For vital upper atmospheric data, forecasters rely on information from weather balloons that are launched twice a day and continuous, automated reports of atmospheric pressure, temperatures, and wind speeds and directions from many airliners. Pilot radio reports of current weather radioed to flight service stations add to the data flow.
All of this data goes to the NWS Center for Weather and Climate Prediction in College Park, Maryland (and similar centers in other parts of the world), where supercomputers programmed with forecasting models use the data to produce a huge variety of forecasts as tables of data, words, and various kinds of weather maps.
One of the first things you need to understand is which weather products are reports of past data and which are forecasts. Meteorologists call a map based on reports of the actual weather at a certain time in the past an analysis. Maps and words presenting forecasts of the weather at a particular time or times in the future are called progs, for prognosis.
FORECASTS DON’T AGE WELL. The National Service makes some kinds of forecasts for days and even months ahead, but the only pilots who need an aviation weather forecast for more than a half-day ahead are those planning long over-ocean flights. This is just as well: A basic principle of weather forecasting is that the further ahead the forecast is for, the higher the probability it will turn out to be wrong.
Many of the longer-range forecasts—such as a NWS general forecast for the public for five days ahead—will say something such as “afternoon showers” without attempting to say when the showers are likely to begin and end. That’s OK. No one should be making important decisions based on such a forecast that far ahead of time. Pilots need much more specific information, but they need it for maybe five hours—not five days—in the future.
PREDICTIONS ARE GETTING BETTER, NOT PERFECT. The National Hurricane Center predicted five days in advance that Hurricane Sandy would come ashore in southern New Jersey on October 29, 2012, with major wind and flood damage from New England to Maryland. In some ways, the paths of big storms such as Sandy are easier to predict days ahead of time than smaller-scale events such as the ceiling and visibility at a particular airport at a certain time. This is because large-scale weather patterns, such as jet stream winds across North America and the Atlantic, affect the paths of storms such as Sandy. These are often more predictable than the smaller-scale factors that affect local ceiling and visibility.
Local ceiling and visibility are easier to forecast at certain times than at others. For example, if you’re making a cross-country flight on a day when a large surface high-pressure area is dominating the region, a terminal aerodrome forecast (TAF) for your destination is likely to hold up well for a few hours. If the weather is forecast to change as an extratropical storm moves toward the area, on the other hand, you should be alert for poorer visibility or a lower ceiling if the storm moves faster than expected.
THE STANDARD BRIEFING. Learning how to collect weather information for flights begins with becoming familiar with the FAA’s Standard Weather Briefing. Such a briefing ensures you will obtain the required information. The elements are:
- •Reports and forecasts of adverse conditions
- If a visual flight rules flight is not recommended
- A synopsis, which is a brief description of the weather
- The current weather conditions
- An en route forecast
- A destination forecast
- The winds aloft forecast
- Notices to airmen
Obtaining the current weather as well as forecasts helps you see how the weather is expected to work out. For example, if the current weather at your destination airport is low ceilings with rain showers, the synopsis might tell you that a weak cold front is moving across the airport now and is expected to have moved on, leaving clearing skies by the time you expect to arrive. If a front or other potentially troublesome weather isn’t moving toward your planned route, you should be safe to take off.
If you aren’t ready to take off for more than an hour or so after your briefing, you should obtain an update right before departure. Call a flight service station at 800-WX-BRIEF (992-7433) and ask for an update briefing. If the forecast is still for conditions to be good when you expect to arrive, go ahead and take off.
On the way you should be alert to any signs that the weather might not be working out as forecast. For example, if the winds aloft are not what was forecast, it could be a sign that other parts of the forecast might also turn out to be wrong.
If you have any question once you are in the air you can radio Flight Watch on 122.0 MHz, or flight service on one of the other frequencies listed on aeronautical charts, and ask for a weather update. Even if you have no particular reason to think the forecast might be wrong, it’s a good idea to call Flight Watch for a weather update when you still have time to turn around or land elsewhere if the weather isn’t cooperating with your plans.
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