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A weather map illustrates the meteorological conditions of an area at a specified time. Weather maps may show cloud cover, storms, precipitation and severe weather patterns as well as air pressure isobars and air temperature isotherms. In recent decades, better weather instruments as well as radar systems and weather satellites have facilitated the production of weather maps and improved the accuracy of weather forecasts.
Reading A Weather Map
What do you see when you look at a weather map? The first thing you should look for are the areas of high and low pressure. The centers of these high and low pressure weather systems are labeled "H" and "L," respectively.
You'll also want to look for isobars. Isobars are lines of equal air pressure; in most cases they are labeled with a number that represents the air pressure in hectopascals, or millibars. The air pressure is higher near the center of a high-pressure weather system, while it is lower near the center of a low-pressure system.
You can tell a lot about the weather by the isobars' proximity to each other. Isobars that are closely spaced mean strong winds, which usually go hand-in-hand with low-pressure systems. Bars that are spaced far apart generally indicate calm, high-pressure systems. In other words, blue skies!
The isobars will also show how the winds are flowing around the primary highs and lows on a weather map, as well as whether they are drawing in air from lower or higher latitudes. In the Northern Hemisphere, wind flows in a counter-clockwise direction around lows and in a clockwise direction around highs; in the Southern Hemisphere the opposite is true. By following the isobars out from the center and determining the wind direction, you can tell where the wind is coming from.
These air flow patterns are important, because a wind's direction and source will greatly influence the type of weather it brings. For example, air from high latitudes in winter is cold and dry, while air drawn from low latitudes will be humid and warm.
Weather maps can also show boundaries between air masses of differing temperatures. These boundaries, called fronts, are indicated by cold front and warm front lines. Cold fronts are indicated by lines with triangles; warm fronts are indicated by lines with hemispheres. In most cases, frontal systems will bring weather changes.
The ability to read a weather map will make weather forecasts easier to understand and more informative. Most newspapers feature fairly simple weather maps. Some of them show isobars, while others do not. Most newspaper weather maps do show primary high and low pressure areas as well as cold fronts, warm fronts, and stationary fronts.
To learn even more about the weather, many people now use both weather maps and satellite images. While satellite images show cloud formations, weather maps show how the weather is moving, where the air masses are coming from, and where the fronts are. Used together, it's easy to see how the atmosphere creates weather! This knowledge of weather allows people to see dangerous weather patterns such as snow storms and tropical storms before they arrive, so that protective measures can be taken.
WeatherMap.us features weather forecast maps and a satellite weather map of continental United States. The website also features maps showing current weather conditions, weather forecasts for specific zip code locations, and links to selected weather resources.
Weather Radar Maps
Weather radar uses pulsed microwave radiation pulses to detect various degrees and forms of precipitation including light rain, heavy rain, snow, and hailstones. In some cases, Doppler radar is also used to determine wind velocities and directions. For local and regional Doppler radar maps and images, visit the National Weather Service Doppler Radar page.
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