Throughout the world, time weather observations are always referenced to Coordinated Universal Time or Universal Time Coordinated, also known as Universal Time or UTC. The military generally refers to it as Zulu Time or "Z Time." This international time standard was known as Greenwich Mean Time (GMT) prior to 1972, and UTC is still based on the 0° longitude (Greenwich) meridian that passes through England's Greenwich Observatory.

Maintained by the Bureau International des Poids et Mesures (BIPM) in Paris, Coordinated Universal Time is the basis for legal time worldwide, including weather observations. By the authority of the Convention of the Metre, a diplomatic treaty between fifty-one nations, the BIPM ensures world-wide uniformity of measurements and their traceability to the International System of Units (SI). The Convention mandates that time weather observations taken by Member States be recorded using UTC in 24-hour format, i.e. 0000 for midnight, 1300 for 1:00 PM, 1800 for 6:00 PM, etc.

Worldwide, official local standard time is referenced as the number of hours from UTC, depending on the number of time zones a particular locality is distant from the 0° meridian. For example, in North America the Eastern Time Zone is five time zones away from the Greenwich meridian (UTC -05:00) and consequently five hours later than UTC. Midnight (0000) Eastern Standard Time is 0500 hours UTC, five hours later than EST. Even with home weather stations, personal time and weather is not an acceptable official time and weather reference. Coordinated Universal Time is never adjusted to Daylight Savings Time, so with the advance of one hour when DST goes into effect the Eastern Time Zone is only four hours later than UTC.

The international weather and time standard of Coordinated Universal Time is used by many interests outside of the meteorological community: astronomers, radio operators, international airlines and shipping companies to name a few. And the radio controlled clock you may have in your home is updated daily using UTC.

 

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