When the tower controller, the ATIS or a METAR says Wind 270, 15 knots does it mean the wind is blowing in the westward or in the eastward direction?
Is there a single convention used to express the wind direction?
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$\begingroup$ Wind direction in what? METAR? $\endgroup$ – aeroalias Mar 30 '16 at 19:07
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$\begingroup$ @aeroalias: METAR, ATIS, or by the tower if that matters. $\endgroup$ – mins Mar 30 '16 at 19:09
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1$\begingroup$ You know, I've been meaning to ask this for ages. Thanks for picking up my slack!! $\endgroup$ – FreeMan Mar 31 '16 at 13:13
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$\begingroup$ @mins, I find it amazing that someone who asked such a seemingly basic question just 3½ years ago now is one of the top-players here on AvSE. This is just great. $\endgroup$ – PerlDuck Nov 17 '19 at 15:26
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1$\begingroup$ I wouldn't call that sad. In hindsight these questions are trivial, but they weren't by the time they were asked. A good question is one that hasn't been asked before. $\endgroup$ – PerlDuck Nov 17 '19 at 16:24
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As far as METARs are considered, the wind direction gives the direction from which the wind is coming. From METAR definitions:
Wind Direction.
The direction, in tens of degrees, from which the wind is blowing with reference to true north.
So, Wind 270 shows that the wind is coming from west.
The reporting in ATIS and tower is the same, only difference being that the reference is magnetic north, while it is true north for METAR.
answered Mar 30 '16 at 19:13
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2$\begingroup$ Great. What does "coming from" even mean... Is it pointing west, or is it pointing east? Raaahhh! $\endgroup$ – Zizouz212 Mar 30 '16 at 23:28
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9$\begingroup$ I think "Coming from the west" means "the air molecules are coming from the west". $\endgroup$ – AMADANON Inc. Mar 30 '16 at 23:49
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2$\begingroup$ Does this mean that a "Nor'easter" is coming from the North East? $\endgroup$ – FreeMan Mar 31 '16 at 13:14
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3$\begingroup$ @FreeMan Yes. At least on/near land it blows from northeast to southwest, hence the name. Though a Nor'easter is a cyclone-style swirling air mass, so the wind direction you feel depends on where in the swirl you are. But again, its name comes from the wind you feel on land, and that'll be a nor'easterly wind. $\endgroup$ – Flambino Mar 31 '16 at 14:41
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1$\begingroup$ thanks, @Flambino. One of those things that seems obvious until you think about it a bit, then you start to wonder... :) $\endgroup$ – FreeMan Apr 4 '16 at 14:38
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Wind numbers say where the wind is coming from. Wind 270 means that the wind is coming from the west, and blowing towards the east. If you point west (270), you will have the wind in your face as a headwind. If you point east (270 - 180 = 90), you will have a tailwind, or the wind at your back.
Another way to think about this is if you want to take off from runway 27, where you are pointing to 270, (pointing west), you want the wind coming from 270, so that you have a headwind.
It's easy to remember that when you are on runway 27 you are pointing to 270. Just remember that a headwind aligned with the runway will have the same number, and you will remember that the wind direction is where it is coming from.
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8$\begingroup$ Yet another way to think about it - an old fashioned weather vane will point into the wind, and it's an easy instrument to read $\endgroup$ – Dan Pichelman Mar 30 '16 at 19:49
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I always use the old saying;
The North wind doth blow, and we shall have snow...
Since this saying originated in England and in England it is colder to the North, we can conclude that a North wind blows from the North.
Incidentally, it is precisely the opposite with ocean currents. The Gulf Stream is a North-Easterly current, because if you are floating in it, it will take you to the North-East.
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5$\begingroup$ "opposite with ocean currents", interesting point indeed. $\endgroup$ – mins Mar 31 '16 at 8:13
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$\begingroup$ @mins it comes from the fact that for a boat, the direction the current is taking you is what you care about. For both a sailing boat and a plane, the direction the wind is coming from (and therefore passing over the sails/wings) is what matters. So we report both as the "most useful" version $\endgroup$ – Jon Story Apr 1 '16 at 13:00
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$\begingroup$ @JonStory: If the wind direction was the direction the molecules go to, one could have said: For a crosswind what's important is the direction the plane will be swerved to, and that would just be an argument against the current convention. $\endgroup$ – mins Apr 1 '16 at 17:18
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As a pilot, you really want to know the wind direction on takeoff and landing. The reported direction will be where the wind is coming from, that is, opposite the direction the windsock is pointing. A good rule of thumb is that if the direction is reported in writing (METAR) then the bearing is relative to true north; if by voice (ATIS) then relative to magnetic north. This makes sense from the perspective that ATIS is related to a specific airfield, whose runway directions will be numbered according to the local magnetic variation. At an untowered field, pick the runway numbered closest to the ATIS-reported direction.
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$\begingroup$ Carlo, it would be helpful if you provided clarification of your review. How did I not answer the question? If the asker has ever seen a windsock, then "coming from ... opposite the direction the windsock is pointing" seems like a pretty obvious mental picture. Also, none of the other answers specifically articulated the "written vs. spoken rule", which is what I was searching for when I arrived here. $\endgroup$ – kerlyn Feb 12 '19 at 0:54
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$\begingroup$ While not an absolute answer, or even trying to be, this answer provided some useful information and context that other answer did not. $\endgroup$ – Reid Apr 12 '19 at 23:38
