WX BRIEF

Using global met resources

Access to weather information from almost anywhere in the world is just a few clicks away.




Standard grayscale infrared satellite image of ICAO Region F (Pacific Ocean)

This shows up on a satellite image as white (lots of water vapor) or black (low water vapor).

Such information is useful in flight planning because it can tell you the potential for cloudiness, convection and precipitation—for example, whether very humid air is being drawn in from the coast and into an approaching cold front.

A single satellite image can provide a snapshot of the current state of the atmosphere over a region, but a series of images can give you a better idea of how the weather is developing.

By looking at the satellite images over the past 8–12 hrs, or even the past day, you can see how fast a weather system is moving, whether it is organizing or decaying, or whether afternoon thunderstorms are popping up.

Quite a few websites offer satellite imagery, and many —such as the satellite imag­ery pages at NOAA's Aviation Weather Center (aviationweather.gov/obs/sat/ intl/), NASA's Marshall Space Flight Center (weather.msfc.nasa.gov/GOES/) or NOAA's National Hurricane Center (nhc. noaa.gov/satellite.shtml)—provide animated image loops for many parts of the world.

Also useful are upper air charts. Weather balloons are launched simultaneously around the world, and that information goes into making global upper air maps, such as a Northern or Southern Hemisphere 300-mb (hPa) map that shows the undulations in the polar jet streams.

Because the free atmosphere is not affected as greatly by localized surface conditions, it can be fairly accurately estimated across regions where no balloons were launched. Such information is extremely useful for figuring out winds aloft, freezing levels and areas of possible bad weather over observation-sparse regions.

Colorized infrared image of Region G (Asia). Grayscale imagery gives better contrast of clouds and identifying weather systems, while colorization helps with differentiating temperatures, such as the blues indicating cold cloud tops and deeper reds representing heat coming from the surface. Satellite images are a great way to evaluate weather conditions quickly along an international flight route.

Lastly, beyond current and climatological conditions, weather forecasts are available for a great deal of the planet thanks to computer forecast models. These models take in as much current observational data as possible from anywhere in their domain and apply the observations to a series of equations that estimate future conditions at points on a regularly-spaced grid.

Because the forecast conditions are interpolated to the grid, rather than just to the locations that provided the initial data, the gridded domain does not exclude locations that did not have any initial observations, although the forecast may not be as accurate as over a region with lots of initial observations.

By virtue of the gridded output of these numerical models, a weather forecast can be obtained for sparsely populated regions, or locations that may not have direct observations or whose station may be out of service. For example, at the time of writing, the weather station at Bektauata, Kazakstan has been out of service for over 11 days, but a current forecast is available courtesy of the computer models.

Furthermore, the models don't just produce forecasts for the surface. Their calculations cover the entire lower atmosphere to the lower stratosphere. As a result, these models can predict conditions aloft with reasonable accuracy and can help a pilot figure out where potentially adverse conditions might be developing.

Expert guidance

While the Internet will provide a lot of international weather information, pilots and dispatchers from countries where local weather information is significantly ad­vanced should exercise caution.

For example, over the US, adds.aviation.gov and other private companies routinely provide such nuanced products as freezing-level or icing-potential maps. These products greatly enhance our understanding of the weather picture along our route, but they are generally not too common over other parts of the world. Instead, only raw or model output data may be available, and it may not be easy for non-meteorologists to interpret.

In addition, Metars in the US and most of the rest of the world differ in units and formatting, increasing the potential for misinterpretation. In most cases, it is wise to seek the expert guidance of an international flight handler.

Using the Internet to gain an initial overview of international weather is a great first step to understanding what sort of weather you'll be facing, but unlike a quick hop to the next state, you will probably have to deal with several different weather systems on a 10,000-mile globetrot, and the meteorologists who do international weather briefings for a living will likely be able to give you a level of guidance you'd be hard pressed to simply glean off of a set of weather maps.

Karsten Shein is a climatologist with the National Climatic Data Center in Asheville NC. He formerly served as an assistant professor at Shippensburg Unversity. Shein holds a commercial license with instrument rating.


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