How Are Isobars Predicted?

Isobar Maps

• Every day, the U.S., Weather Service sends up hundreds of balloons equipped with weather recording devices. One of the most important attached items is the barometer, a meteorological device that measures atmospheric pressure. Next, the valuable information is transmitted to ground personnel, who compile the data to make a weather map. In essence, each barometric reading becomes a dot on the map. Points with equal atmospheric readings are connected to form a line. When all the dots are connected, the resulting map usually consists of numerous concentric circles that somewhat resembles a contour map. Each continuous line is known as an isobar.

Low and High Pressure

• A weather map consists of many of low and high pressure systems, each one represented by a series of circular markings, labeled with a numerical value. Most pressure systems are labeled with an H for high or L for low, but you can read the isobars yourself to see how this works. In general, weather maps are static pictures as they represent how the air pressure reads at one point in time, but weather is different. It never stays the same because the low and high systems move around on the surface of the Earth.

Weather forecasting

• Weather forecasters do not so much predict the movement of isobars, but instead are looking at the movement of complete pressure systems. On a weather map, these systems are diagrammed by the shape and arrangement of isobars. For instance, if the weatherman thinks a low system will intensify as it travels west to east across the U.S., he will be expecting the graphic representation of the isobars to look different after 48 hours. On a weather map, a stronger low system will have isobars that are closer together.

Weather Movement

• One of the primary forces that determines movement of weather systems is the rotation of the Earth. Since the Earth spins in a clockwise position (when looking down from above the north pole) , weather systems tend to move west to east. However, to complicate things there are other factors, such as the jet stream, large landforms and stronger weather patterns, which can cause variations in the movement of a particular weather system. With the aid of computers meteorologists use this information to predict the future strength and location of a weather system.