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Predicting the Weather: Tools, Maps & Symbols

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

How do weather forecasters predict the weather? What tools are used? When you look at a weather map, what do all the symbols mean? Learn about predicting and mapping the weather in this lesson.

Tools for Predicting the Weather

We've all been there. You go out on a sunny day, drive somewhere for a few hours, and then when you get back you find yourself caught in the middle of a violent thunderstorm. You don't have a coat or an umbrella and have to run through the pouring rain.

Even if you check the weather forecast, it isn't always right. Predicting the weather is really hard. But they still get it right far more often than they get it wrong. How do they do that? What tools and techniques are used to predict the weather?

Weather is the atmospheric conditions of a place on earth at a particular time. These conditions can be hot or cold, rainy or dry, windy or calm. Weather is all about collecting data. The atmosphere is chaotic and complex, but by having lots of data about the past we can recognize patterns and use them to predict the future.

We collect data using various tools. For example,

  • thermometers indicate the temperature,
  • barometers measure air pressure
  • rain gauges indicate us how much precipitation has fallen
  • wind vanes measure the speed and direction of the wind
  • weather balloons float up into the atmosphere and get an idea of what's going on up there, and
  • weather satellites see what's going on in the atmosphere from above.

Altogether this brings a wealth of data, and we have been collecting this data for many years.

Weather balloon
Weather balloon

From the data we can look for patterns. For example, meteorologists (experts in weather) can look at the movement of cold fronts and warm fronts and compare it to what they have seen in the past.

When cold air is replacing warm air, it's called a cold front. This causes temperatures to drop, and tends to lead to heavy thunderstorms.

When warm air is replacing cold air, it's called a warm front. This causes temperature and humidity to rise. Fog can result, followed by rain as the front passes. The movement of these fronts and other types is related to air pressure, so measurements of air pressure are also useful. When the fronts pass, they tend to leave clear skies behind them.

The lay of the land is also important: the presence of mountains, lakes, and seas have a big influence on how air moisture moves. Comparing what is observed to historical averages can give a good idea of what's going to happen.

Weather Maps and Symbols

Once you come up with your prediction, you have to communicate it to people. Those people could be other meteorologists, or the public through a weather report. We have standard ways of doing that. Showing weather almost always involves a map, with lots of symbols on top of it.

Weather Map
Weather Map

One kind of symbol you might see is an arrow to show the wind speed and direction. A big, bold arrow can mean faster wind speeds. Another thing you might see are numbers to show the temperature at different locations. And you might also see an L or H to show low pressure and high pressure areas, with solid lines to show areas of constant pressure.

But perhaps the most complex kind of symbol on a weather map are those that show hot and cold fronts. A warm front (#1 on the diagram below) is shown with a red line that has red semicircles connected to it. A cold front (#2 on the diagram below) is shown with a blue line that has blue triangles connected to it - it looks a bit like triangle flag bunting you might see on the streets during a festival or at a party.

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