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Weather Help

Help with terminology or return to Weather.

Satellite Imagery:

For more information see: Interpreting Weather Satellite Images.


What is GMT?

Greenwich Mean Time or GMT is the time standard against which all other time zones in the world are referenced. It is the same year round and is not effected by Daylight Savings Time. GMT is the north-south meridian at zero degrees longitude, or the "prime meridian", that runs through the Greenwich Observatory near London, England (where the system originated). GMT is used synonymously with Z (Zulu time), which stems from the military ("Zulu" is the radio transmission articulation for the letter Z). GMT is sometimes used interchangeably with UTC (Universal Time Coordinated). UTC or UT (Universal Time) is based on an atomic clock, and is therefore not exactly the same as GMT, which is based on mean solar time, but the difference is very small. UTC replaced GMT as the time standard, but GMT is still widely used today.

GMT Eastern Daylight Time
Eastern Standard Time
Central Daylight Time
Central Standard Time
Mountain Daylight Time
Mountain Standard Time
Pacific Daylight Time
Pacific Standard Time
Difference (in hours) - 4 - 5 - 5 - 6 - 6 - 7 - 7 - 8
00 8 PM 7 PM 7 PM 6 PM 6 PM 5 PM 5 PM 4 PM
06 2 AM 1 AM 1 AM 12 AM 12 AM 11 PM 11 PM 10 PM
12 8 AM 7 AM 7 AM 6 AM 6 AM 5 AM 5 AM 4 AM
18 2 PM 1 PM 1 PM 12 PM 12 PM 11 AM 11 AM 10 AM

Colorado: Mountain Standard Time (MST in the northern hemisphere Winter) is 7 hours earlier than GMT and Mountain Daylight-Savings Time (MDT in the northern hemisphere Summer) is 6 hours earlier than GMT.


Commonly Used Acronyms & Abbreviations




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Special thanks to Scott Bachmeier, Research Meteorologist and Wx-weenie friend,
Space Science & Engineering Centre, for his comments.

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