Although languages may differ from one country to another, the weather recognizes no national border. The United Nations set up an agency called the World Meteorological Organization (WMO) to see that the weather information is collected and transmitted with uniformity from one part of the world to another. The WMO consists of 130 nations. Each is required to collect data at certain times and transmit the information in a universal code. The times for collection are based on Universal Time (UT), or Greenwich Mean Time (GMT), which is the local time at the Greenwich Observatory in England. The radiosonde data is collected at 1200 GMT (noon at Greenwich) and 0000 GMT (midnight). Local times depend on the longitude of other locations. Every 15 degrees of longitude away from Greenwich is another hour different. Greenwich is used as a standard because it's located at zero degrees longitude, the prime meridian.
GMT—Greenwich Mean Time—is the local time in Greenwich, England, and is measured on the prime meridian (zero degrees longitude). Meteorological and navigational clocks are set to GMT so there will be uniformity in reporting the time of data observation and collection.
After an observation is taken, it's immediately transmitted by teletype, radio, or satellite. The data is collected at several worldwide centers and then processed and retransmitted to the multitude of users. At these centers, such as in Washington, D.C., the data is analyzed and put into super computers that draw charts and project future patterns.
The data is transmitted in a special code and plotted in a particular format on weather maps.