Wind Direction: METAR and ATIS
I noticed that at our field the reporting of the METAR wind direction and the ATIS wind direction have been the same. I was taught long ago that if you hear it, it’s magnetic and if your read it it’s true. So what’s up?
I emailed the tower manager and it turns out that they are doing it wrong. If I understand his reply our ASOS has had a magnetic variation calculation built into it since at least 2013 but for some reason the controllers are not reading the correct data from it. All of those sites I mention below are ASOS sites, same as SBP. Sites with AWOS require a manual calculation for magnetic variation.
It is still true, that for wind direction if you hear it it’s magnetic and if you read it, it’s true but I with the advent of graphical forecasts we probably need to adjust the saying a bit. If you hear it, it’s magnetic and if you see it, it’s true. The exception being PIREPs which are generated by pilots using magnetic indicators in the cockpit like VORs and compasses. And now, with D-ATIS
Digital – Automatic Terminal Information Service printed out in the cockpit at some airports, it needs a slight adjustment to the saying.
What I observed using ForeFlight and calling up the ATIS at various airports was:
The wind right now (2024-04-29 2:59 PM) is reported the same on the METAR and the ATIS recording.
ATIS 2156Z 320 at 22 gusts 30
METAR KSBP 292156Z 32022G30KT
I would expect the ATIS to be more like 310 correcting for the magnetic variation of 12°30’E.
Santa Barbara has a magnetic variation close to 12°15’E.
ATIS 2153Z 140 at 5
METAR KSBA 292153Z 15005KT
Livermore magnetic variation is 13°E
ATIS 2153 260 at 9
METAR KLVK 292153Z 28009KT
Just for fun I looked up the definitions on various FAA publications.
Aviation Weather Handbook
24.3.1.2 ASOS Reporting
Note: National network distribution (e.g., FSS, internet, and FIS-B) of wind direction is in true degrees, while local dissemination (e.g., radio and telephone) is in magnetic degrees.
24.4.3 METAR/SPECI Format
24.4.3.5 Wind Group
In the wind group, the wind direction is coded as the first three digits (220) and is determined by averaging the recorded wind direction over a 2-minute period. It is coded in tens of degrees relative to true north using three figures. Directions less than 100° are preceded with a 0. For example, a wind direction of 90° is coded as 090. A wind from the north is coded as 360. Immediately following the wind direction is the wind
Pilot’s Handbook of Aeronautical Knowledge
Aviation Routine Weather Report (METAR)
Wind—reported with five digits (14021KT) unless the speed is greater than 99 knots, in which case the wind is reported with six digits. The first three digits indicate the direction the true wind is blowing from in tens of degrees.