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Old July 3rd, 2009, 02:22   #18
clestudentpilot
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Join Date: May 2007
Posts: 95
Default Re: ATIS Winds - True or Magnetic?

It is not always true in print that the winds are true. Where I was at, it was a manual weather reporting station. The instruments they read the winds from were the same whether you were writing down the METAR information to record the ATIS, and to call FSS with, or giving it to pilots in a takeoff or landing clearance. While this contradicts things, I asked some people who are much more knowledgable than I am when it comes to being a whether observer, since I am not one, I received the answer that the NWS prefers true, the FAA prefers magnetic. The NWS has won out in these scenarios. To obtain a wind reading, you observe the wind for 2 minutes, and take the average of the 2 minute reading. I won't get into details on gusts factors, or variable wind directions. When an automated station give the winds, whether on a frequency on ASOS or AWOS, or in a METAR, the same is true, a 2 minute average. The automated stations are obviously much more accurate, and the machine can automatically change the direction for magnetic direction in an AWOS or ASOS recording you listen to. At controlled fields, they may have to look at the METAR readout from the AWOS, and convert before recording the ATIS. For all intents and purposes, a human weather observer just is not good enough to get the very precise winds when observing them. If the winds cary between 176 and 224 in the 2 minute interval, the observer may to average it say it varied between 170 and 230 to give a wind of 220, while someone else may see this as between 180, and 230 for 225, which would round to 230. What I'm saying is that humans just aren't good enough at the manual stations to get it as accurate as the automated stations can. That is why we didn't add or subtract anything when calling FSS with the METAR, it was so close that it was impracticle. Stations in Maine or Washington may do things differently though
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