National Weather Service Glossary
This glossary contains information on more than 2000 terms, phrases and abbreviations used by the NWS. Many of these terms and abbreviations are used by NWS forecasters to communicate between each other and have been in use for many years and before many NWS products were directly available to the public. It is the purpose of this glossary to aid the general public in better understanding NWS products.
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- The phenomenon of the sun's daily disappearance below the western horizon as a result of the earth's rotation. The word is often used to refer to the time at which the last part of the sun disappears below the horizon in the evening at a given location.