Term
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Definition
The visibility that is considered representative of visibility conditions at the station; the greatest distance that can be seen throughout at least half the horizon circle, not necessarily continuous. |
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Term
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Definition
The visibility in a specified direction that represents at least a 45 degree arc of the horizon circle. Sector visibility shall be reported in remarks when it differs from the prevailing visibility by one or more reportable values and either the prevailing or sector visibility is less than 3 miles |
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Term
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Definition
The prevailing visibility determined from the usual point of observation. If visibility observations are made from just one level, e.g., the airport traffic control tower, that level shall be considered the "usual point of observation" and that visibility shall be reported as surface visibility. For automated stations, represents 10 minutes of sensor output. |
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Term
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Definition
The prevailing visibility determined from the airport traffic control tower (ATCT) at stations that also report surface visibility. |
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Term
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Definition
dark or nearly dark objects viewed against the horizon sky shall be used during the day, and unfocused lights of moderate intensity (about 25 candela) shall be used during the night as reference points for manually determining visibility. In addition, visibility sensors may be used to assist the observer in the evaluation. |
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Term
| Variable Prevailing Visibility |
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Definition
If the prevailing visibility rapidly increases and decreases by 1/2 statute mile or more, during the time of the observation, and the prevailing visibility is less than 3 miles, the visibility is considered to be variable. |
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Term
| Visibility at 2nd Location |
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Definition
When an automated station uses a meteorological discontinuity visibility sensor, remarks shall be added to identify visibility at the second location which differ from the visibility in the body of the report |
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Term
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Definition
the maximum distance at which the runway, or the specified lights or markers delineating it, can be seen from a position above a specified point on its center line. The location of the RVR visibility sensor should be within 500 feet of the runway centerline and within 1,000 feet of the designated runway threshold RVR shall be reported whenever the prevailing visibility is 1 statute mile or less and/or the RVR for the designated instrument runway is 6,000 feet or less. RVR is measured in increments of 100 feet up to 1,000 feet, 200 feet from 1,000 feet to 3,000 feet, 500 feet above 3,000 feet to 6,000 feet. Up to four RVRs if automated, only 1 if manual. Use light setting 5 for transmissometer systems |
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