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Why is it that a winds aloft forecast normally has a "valid time" that comes in the middle of the "for use" time range? Why don't they just state the valid time as the beginning of the for use time period? It says it is valid starting at 1800 but its for use time starts four hours earlier, why?

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  • $\begingroup$ Welcome to aviation.SE! To make your question as clear as possible, it would be helpful to add a specific example. $\endgroup$
    – Pondlife
    Jun 20, 2021 at 15:35

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Wind and temperature aloft forecasts (FB) are computer-prepared and issued by the National Centers for Environmental Prediction (NCEP) at Suitland, Maryland. The forecasts are valid 6, 12, and 24 hours after the observation date/times of 0000Z, 0600Z, 1200Z, and 1800Z based on National Weather Service Instruction 10-812, Aviation Wind and Temperature Aloft Forecasts.

Source: FAA 7110.10

In essence, it's a subtle way of telling you it's a best guess based on observations and computer models, and it covers a time period where they think the model's conclusion will be closest to the real thing. Like medicine, weather forecasts are not an exact science.

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  • $\begingroup$ I think my English is pretty clear. $\endgroup$ Dec 21, 2021 at 20:13
  • $\begingroup$ Well, like, now it is 😃 $\endgroup$
    – Jpe61
    Dec 21, 2021 at 23:00
  • $\begingroup$ Second, slower readings always seem to help, don't they... $\endgroup$ Dec 22, 2021 at 20:59
  • $\begingroup$ I concur. The original wording was, however, not as clear as the edited one. $\endgroup$
    – Jpe61
    Dec 22, 2021 at 22:22
  • $\begingroup$ The wording of the last paragraph never changed. Anybody can see that. I consider this subject closed. $\endgroup$ Dec 24, 2021 at 0:03

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