Weather

Since the 1980s, the federal aviation regulations have required teaching pilots how to use good judgment—aeronautical decision making (ADM)—as a critical skill needed to avoid accidents.

Such programs were developed first to teach air carrier flight crews (everyone, not just the pilots) crew resource management philosophy and techniques for using all available resources, including all crewmembers and other people such as air traffic controllers, hardware, and information to make flight decisions.

The FAA and flight schools have adapted these techniques to single-pilot resource management (SRM), which focuses on managing all of the resources available to a single pilot both before and during a flight. These resources include weather information.

Introducing weather products. The National Weather Service and private meteorology companies produce two types of weather products to help pilots make weather decisions: reports of what the weather is doing now or in the very recent past, and what it’s predicted to do in the next few hours.

Meteorologists use weather data going back as much as 30 years to compile climate information based on weather averages. These aren’t of much use to pilots unless they’re looking for a place with mostly sunny skies and few storms to affect flight training. However, the weather along a planned route of flight for the last few hours is important because it sets the stage for the weather you’re likely to encounter during a flight.

While meteorologists make forecasts for days, weeks, and months in the future, the only predictions pilots should use are the most recent ones for the times of the flight.

Worded reports of weather data are called observations. If the observations are used to produce a map, the map is called an analysis.

Worded reports and maps of forecasts often are called “progs” (for prognoses). The NWS produces significant weather prog maps showing expected locations of dangerous weather for as much as 24 hours in the future.

Weather depiction charts. If you plan to take off in the next hour or so, you should begin by looking at the current weather and then turn to forecasts of how it’s expected to change. At times, a look at the current weather could make you decide to bag your flying plans for that day because it’s obvious that a big storm along your route isn’t going to disappear before you want to take off.

The NWS weather depiction chart (top left) gives you a quick overview of the weather that most affects pilots.

If you do not have an instrument rating, you must avoid the areas shown on the chart with instrument flight rules (IFR) conditions. These areas have ceilings below 1,000 feet and/or visibility less than three miles. They are outlined on the chart with a shaded area inside a solid line. On color versions of the chart, IFR areas are shaded in red.

You could fly legally in areas with marginal VFR without an instrument rating if you stayed far enough away from clouds, but marginal VFR weather could quickly deteriorate into IFR weather.

Weather depiction charts outline marginal VFR areas with a solid line, but areas inside the lines are not shaded. Marginal VFR means ceilings are 1,000 to 3,000 feet above the ground and/or visibility is three to five statute miles. Areas not inside a solid line on the chart have either clear skies or ceilings higher than 3,000 feet and visibility greater than five miles.

The circles on the map represent airports; the shading indicates ceiling. Solid black dots show the sky is overcast, while all-white circles mean clear skies. Partly shaded circles show scattered or broken clouds. You can see that on the day the chart was produced, IFR and marginal VFR weather covers most of the eastern United States.

Surface analysis charts. While the weather depiction chart displays areas of IFR, MVFR, and VFR weather, surface charts (top right) add to the picture by showing the major weather features that are causing those conditions.

The thin red lines on the map are isobars, which represent areas of equal barometric pressure. The “Ls” are centers of relatively low surface atmospheric pressure, and the “Hs” are centers of relatively high pressure. The most prominent weather feature on this chart is the area of low pressure centered a little to the southwest of where the borders of Alabama, Georgia, and Tennessee meet.

If you look off the South Carolina coast on the chart, you’ll see text in red that identifies this strong low-pressure area as the center of Tropical Depression Ivan, which had come ashore as Hurricane Ivan the day before near Pensacola, Florida.

The chart’s other prominent feature is the blue line with blue triangles stretching from northern Canada to the southwest across western New York, central Ohio, and into Arkansas. This is a cold front in which cold air is advancing toward the southeast. Across Oklahoma, the cold front becomes a stationary front, in which neither the warm air to the south nor cool air to the north is advancing.

This chart informs pilots from Georgia to New England that the advancing front could bring showers and thunderstorms, and the remnants of Ivan would be moving to the northeast ahead of and roughly parallel to the front with a good supply of humid air to feed precipitation.

Details are in the words. Some NWS word products describe the latest weather observations. Probably the most useful are the METARs for the airport you’ll depart from, your destination, and maybe airports along the route.

METARs are worded reports of observations from airport weather stations, which normally are issued a few minutes before the top of each hour. Weather stations issue special reports for major weather changes, such as a line of thunderstorms moving across the airport. A weather station also will issue a special report if an aircraft crashes at or near the airport. The National Transportation Safety Board uses these for its investigations.

The format follows an International Civil Aviation Organization code, with some differences such as using feet and miles instead of meters and kilometers. The acronym METAR is a rough translation from the French words for “aviation routine weather report.”

To learn more about obtaining weather data for flying, you can begin with Chapter 12 of the FAA’s Pilot’s Handbook of Aeronautical Knowledge, titled “Aviation Weather Services.” To dig deeply into sources of aviation observations and forecasts charts and text, see Aviation Weather Services, Advisory Circular 00-45F.