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Posted at 10:45 AM ET, 03/16/2010

Daylight Saving changes time, not weather

Wx and the City

* The sun has arrived and is here to stay: Full Forecast *

On early Sunday morning, most of the United States, save Hawaii and most of Arizona, sprung an hour ahead to Daylight Saving Time (DST), losing an hour of sleep in the process. However, when it came to weather observations and forecasting, the National Weather Service did not change its clocks this past weekend. Nor will it do so in November.

Hourly weather observations in locations throughout the world fit together like puzzle pieces, showing meteorologists the larger picture of what's going on in Earth's atmosphere at any given time. If times changed twice a year, the records would be inconsistent.

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Instead, official weather observations (measurements of temperature, humidity, wind speed, precipitation, etc.) are recorded using Coordinated Universal Time (UTC), also known as "Zulu" time, which remains consistent throughout the year. UTC has largely replaced Greenwich Mean Time (GMT) as the time system used in science.

On weather forecasting maps and models, as well as satellite images, time is displayed in UTC, usually on a 24-hour clock. For those of us on the East Coast of the United States, Eastern Standard Time (EST, November to mid-March) is five hours behind UTC. Eastern Daylight Saving Time (EDT, mid-March to November) is four hours behind it. A map updated today at "1200Z" or "12:00 UTC" would be valid for "0800 EDT" or 8:00 a.m. (check out this chart and the current regional radar image for examples of the conversion).

Interested in learning more about DST? Here's a great resource.

By  |  10:45 AM ET, 03/16/2010

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