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 alternating red and blue symbols on different sides of the
line. An occluded front, represented as a purple line with alternating triangles and semi-circles on the same side, 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 lowpressure area over the upper Midwest United States.