When you look at isobars and isotherms, it will be easy for you now to see where there are low-pressure systems. In the figure you just saw, low-pressure system was obvious as the area in the center of isobars that decreased in air pressure as you moved toward the center. In fact, whether maps often show two letters indicating high-pressure or lowpressure. If you see the H, is a high pressure air mass. If you see the letter L, it is a lowpressure air mass. Any elongated sections of low-pressure are known as troughs. Any elongated section of high-pressure is known as a rich When you study isotherms on a map, you can often predict where the wind is blowing. If a series of isotherms are very close together, there is a large temperature difference over a short space on the map. Of course, this will be an area where wind will travel across a shorter temperature gradient. The same is true for isobars; if these are close together, winds will be high. We will study surface maps in a minute. You can see however, that these isobars and isotherms provide a good pictorial representation of a lot of the data collected in different parts of the world.
SURFACE AND UPPER AIR CHARTS Now we can study real weather maps. While these are interesting, the real goal of them is to predict what type of weather you can expect in the next hours, days, or perhaps a week or more in length. Meteorologists often show these maps on the news; now you will be able to read them too. What you can now imagine is that people collect information about the current temperature and pressure in their area. This data is put together to create isobars and isotherms. In addition, we have radar to show there are current storms in areas of precipitation. All of this information is put together to make predictions. Many of these weather maps are color-coded so you can see that red areas indicate warmer temperatures while green and blue areas on the map indicate cooler temperatures. You've probably heard of cold fronts and warm fronts. A front is the edge of any moving air mass. Symbols on the surface map will tell you not only if it is a cold front or a warm front, they will tell you the direction the air mass happens to be moving. A stationary front will also be marked in a way that makes it easy to see that the front is not moving.
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