It is essential that all weather stations record observations using a uniform time code. However, local times are different around the world. When it is day where you live, it is night on the opposite side of the planet.
There are 24 time zones around the Earth, one for each hour of the day. Time zones are based on longitude, the imaginary lines that pass through the North and South poles. About every 15 degrees longitude, a new time zone begins. Scientists had to choose an arbitrary starting point for longitudes. This longitude is called the prime meridian, and it passes through Greenwich, England. It is labeled as zero degrees longitude.
To keep people from confusing 5 a.m. with 5 p.m., scientists and meteorologists use a 24-hour clock instead of the normal 12-hour system. On a 24-hour clock, midnight is 0:00 and noon is 12:00. That means 2 p.m. is 14:00. What number would be used for 8 p.m. on the 24-hour clock? You're correct if you answered 20:00.
Some weather reports label time as Greenwich mean time, or GMT. It's also called universal time (UT) or Zulu time (Z). Meteorologists usually use the term, Zulu time. The term Zulu comes from the military term for the letter "Z," which is Zulu. Because Zulu time starts at the prime meridian, or zero degrees longitude, military personnel chose Zulu as the term to indicate zero.
To solve the problem of local time being different at 24 places around the globe, many weather reports change the local time to Zulu time. The following time zone chart shows how Eastern Daylight Time compares to Zulu time.
|Zulu to Eastern Daylight Time|
(Zulu minus 4)