Instructor Tips: Getting Weather from the Web

Becoming a pilot entails much more than just learning how to control an aircraft. Among other things, it means learning about the weather. But for most students, watching weather videos, deciphering METARs and TAFs, and studying surface analysis charts is just not as exciting as shooting touch and goes on a blustery day.

That makes teaching weather a real challenge for instructors. Wouldn?t it be great if we had a tool that could show them real-time, interactive color weather images rather than black-and-white pictures in a textbook? Wouldn?t it be wonderful if we had a tool that would entice students to apply the theory they?ve learned and that would motivate them to learn far more than the minimum required to pass the written exam? Fortunately, we have exactly such a tool at our disposal, and it?s already in millions of households across the nation. It?s simply a personal computer with Internet access.

Begin at the Beginning

A virtual encyclopedia of weather information and a wide range of weather products just for pilots (including DUATs) are readily available free on the World Wide Web. But before you give your students a guided tour of these products, make sure to educate and prepare yourself. Start by having a plan. Bookmark the sites you want to show your students so that you can open them quickly. Be prepared to discuss the relevance, use, and limitations of each of the products that you show them.

As with any good weather briefing, begin with products that show students the synopsis or ?big picture.? The objective here is for students to see broad weather elements and understand that they combine to create local weather conditions. Upper-air forecast charts are a good place to start. Purdue University?s WXP weather server maintains an excellent selection of these forecast charts. [See sidebar for Purdue?s URL address, and those of other Web sites mentioned in this story.]

The 500 millibar (roughly 18,000 feet MSL) constant-pressure charts, for example, show the location and strength of high and low pressure centers, upper-level troughs and ridges, and wind vectors. The 300 mb (roughly 30,000 feet MSL) constant-pressure charts can be used to locate the jet stream. By noting the position of the high and low pressure centers, the wind fields around them, and the location of troughs and ridges, students can see how the upper-air currents steer and provide support for surface weather conditions.

You can also explain how the amplitude of the upper waves is related to the strength of the weather systems they produce. If the amplitudes of the waves are increasing, the surface systems are usually intensifying. Then show your students how the wind speed vectors are related to the distance between the isoheight lines. Where the lines are packed together closely, wind speeds are fastest. Those high wind speeds usually help support surface low-pressure areas. By looking at the 12-, 24-, 36-, and 48-hour forecast charts, students can see how the long, slower moving waves (called Rossby waves) and the short, faster moving waves (called upper-level disturbances) travel from west to east, guiding the surface systems along with them.

Satellite Images

Once your students can recognize the air patterns at the higher altitudes, have them look at satellite images of surface weather systems. They should begin to see the relationships between the upper-air patterns and the surface weather systems.

When you look at satellite images, you will probably see images from one of two functioning Geostationary Operational Environmental Satellites (GOES). One of the most comprehensive Web sites for GOES imagery is maintained by the National Oceanic and Atmospheric Administration (NOAA). The satellite images they offer are extremely useful for locating potential weather hazards, such as low-pressure systems, fronts, thunderstorms, and fog. Show your students how to identify these features on the images.

You should also discuss the three main types of image products available?visible, infrared, and water vapor. Visible images are equivalent to those a human eye would see from space. Visible imagery can show the fine detail of any visible phenomenon, such as cloud coverage, stratus penetration, volcanic ash, or smoke plumes. Students can use the detailed images to accurately locate boundaries between cloudy and clear areas, or separations of different types of clouds such as cumulus, stratus, or towering cumulus. Visible images can also be used to monitor the location and movement of thunderstorms. Of course, visible imagery?s main limitation is that the satellite can produce the images only when the area being scanned is in daylight.

Infrared images, on the other hand, can be made day and night. Using the infrared images, students can see the relative temperature of land, bodies of water, and clouds. Hot deserts appear dark. Warm, low clouds such as stratus appear gray. Cooler clouds, with high, cold tops appear white.

But by far the most amazing products from these satellites are the water vapor images. Water vapor imagery shows otherwise invisible water vapor in the air. Since water is the single most important ingredient in the formation of weather systems?the ?fuel? for the fire?water vapor imagery can be used to track the movement of this fuel. The water vapor channel on the GOES imager responds to water vapor in the middle and upper layers of the atmosphere, typically near 400 mb (approximately 24,000 feet). Thus, these water vapor images are useful for analyzing large-scale flow patterns, including upper-level lows and highs, short waves, and jet streams.

Interpreting satellite images is not difficult, but it is a skill that requires practice. You can refer students who are interested in learning more about satellite images to the training pages available from the Naval Research Laboratory (NRL) and Colorado State University Web sites.

Radar Imagery

If satellite images show that thunderstorms are building, you may want to show your students how to investigate them further with radar. You can find help at sites like Intellicast.com and AOPA.org, which have excellent radar animation pages.

While students are looking at a radar summary graphic, have them find the altitude of the cloud tops, direction of movement, speed, and intensity of the storms. You can also have them identify areas of light, moderate, and heavy rain.

While viewing the animation, ask students whether they think the storms are building or diminishing. This exercise will help them to understand the dynamic nature of weather, and how that can affect a planned flight. For example, 20 minutes can make the difference between an airport being closed due to a thunderstorm overhead, and the same airport being clear and beautiful. Knowing where a storm is headed, and when, enables a pilot to better evaluate options, such as hastening, delaying, or canceling a flight to avoid a storm en route or at the destination.

Of course, no discussion of radar would be complete without mentioning the National Weather Service?s network of 161 Doppler radar sites that cover the entire United States including Alaska and Hawaii. These new Doppler systems, named Nexrad for next generation radar, are so sensitive that they can detect wind patterns in air with no raindrops or snowflakes to reflect the radar energy. With computer enhancement, these systems can discriminate between rain, snow, and hail. They can detect hazardous microbursts, estimate rainfall rates, and even penetrate a storm cell to detect tornadic activity. Students may enjoy the University of Michigan Web site, which provides point-and-click navigation to more than 100 Nexrad radar sites.

Instructing is hard work. Use technology to make your job easier. It?s time to go online.