An important part of studying meteorology is simply paying attention to weather conditions and applying your knowledge to what you observe. However, many different variables including temperature, moisture, cloudiness, precipitation, and others, are used to describe weather. All of these must be considered and analyzed numerically.

Furthermore, the weather at one location is often caused by larger weather patterns. So it is not enough to consider the weather locally. We must also analyze the weather for many other locations. This means even more numbers.
To identify key weather-making patterns, we need to see all the numbers describing weather at many locations, all at once. It is also vital to see how the observations relate to each other geographically. A list of numbers doesn’t help much; we need a picture. So, we plot weather variables on a weather map to understand the relationships among them. To paraphrase the saying, “A picture is worth a thousand words,” a weather map is worth a thousand numbers—or more. In this section, we learn how to interpret weather maps.

Perhaps the most obvious features on weather maps are fronts. A front is a boundary between two regions of air that have different meteorological properties, such as temperature and humidity. A cold front denotes a region where cold air is replacing warmer air. A warm front indicates that warm air is replacing cooler air. All weather maps today depict frontal locations because they are regions of rapidly changing and sometimes dangerous weather conditions. The frontal lines drawn on a weather map represent the locations where the fronts meet the Earth’s surface.

On a weather map, a blue line with blue triangles indicates a cold front. The triangles point in the direction the front is moving. A warm front is shown as a red line with red semi-circles pointing in the direction of frontal movement. A
stationary front is a front that is not moving and is represented as shown in the The occluded front, represented as a purple line with alternating triangles and semi-circles, has characteristics of both cold and warm fronts.

An example of a surface weather map is given above. It includes station model plots and a cold front attached to a low-pressure area over the upper Midwest United States.

Focusing on the station model for Tallahassee, Florida, in the inset above, we see that it is mostly cloudy there, the temperature is 77° F, the dew point temperature is 74° F, the sea-level pressure is 1018.4 mb, the winds are light and from the north, and Tallahassee is experiencing a thunderstorm. The weather observations were all made at the same time. This time is printed in the top right corner of each weather map. Unlike television programming, Eastern Standard Time is not the reference for these maps!