The Wind Vane: Measuring Direction and Gust

The anemometers already published here measure how fast the wind blows. This rung measures where it comes from — which, for forecasting, is the more useful half. A vane is a fin on a bearing with more area behind the pivot than in front, so it weathercocks into the wind. That sounds trivial and is not: a vane that is too light chases every eddy and never settles, one that is too heavy lags real shifts, and one balanced wrongly sits at an angle in a steady breeze. The behaviour you want is a specific amount of damping, and it is a design choice. By convention the direction reported is where the wind comes FROM. A northerly is cold and from the north; the same air moving would be called a southward flow by anyone else. It is a genuine trap and it has reversed more amateur observations than any other rule.