Isobars can form certain patterns, making it useful for weather analysis or forecast. A cyclone or depression is an area of curved isobars surrounding a low-pressure region with winds blowing counterclockwise in its center in the Northern Hemisphere.
An anticyclone is an area of curved isobars surrounding a high-pressure area, and the wind blows clockwise in the center of an anticyclone in the Northern Hemisphere. Open isobars forming a V-shape define a through of low pressure while high-pressured, N-shaped, open isobars define a ridge of high pressure. These features are usually predictable, and associated with certain kinds of weather, making it easier to forecast weather for a particular area.
See also Aerodynamics ; Atmosphere, composition and structure ; Atmospheric circulation ; Barometer ; Weather forecasting ; Weather mapping. The term "isobar" originates from the Greek, isos equal and baros weight. The solid blue contours are isobars and the numbers along particular contours indicate the pressure value of the isobar. Surface maps of isobars are useful for locating areas of high and low pressure , which correspond to the positions of surface cyclones and anticyclones. A map of isobars is also useful for locating strong pressure gradients which are identifiable by a tight packing of the isobars.
Stronger winds are associated with larger gradients in pressure. If the wind direction moves anticlockwise, you have lower pressure. Isobars give you a good indication of what you need to know about air pressure.
Synoptic charts have a few shapes you need to identify, namely lines, triangles, and half-circles. These shapes are known as fronts. If you see a cold weather front, it means there is a change in the air mass. A cold one now replaces the warmer air. It also works the other way around, with warm fronts representing a change from cold to warm.
Warm air is represented by a reddish color scheme, while colder air uses bluish colors. When you look at a synoptic map, you can see either a red or blue line. A warm front uses a red line with red half-circles, while cold fronts use a blue line with blue triangles. The front position depends on factors like temperature and wind direction.
Occluded fronts are when cold fronts catch up with warm fronts, which results in an overlap. The reason this happens is cold air moves faster than warmer air. Occluded front is represented by a purple color scheme, along with a triangle and half-circle near each other. You might see low clouds and light rain underneath these conditions.
You might see black lines with neither triangles nor half-circles. These are known as troughs, which indicate unstable weather areas. Low air pressure moves around at high speeds, which often results in rain showers. They tend to be elongated lines on the map, which resemble a snake trying to slither.
Troughs in the northern hemisphere move in different patterns. For example, upper troughs extend from a low-pressure area in the northeast all the way to the southwest. Lower troughs move the other way around. When you look at a weather chart, be mindful of the isobars. They tell you everything you need to know about projected wind levels. They are plain lines across the weather map, which move in a curved fashion.
You might also see numbers alongside the isobars, which indicate the amount of air pressure. Remember that warm and cold fronts move in specific directions. Warm fronts move clockwise, while cold fronts move anticlockwise.
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