How Do Weathervanes Work?
When the wind blows, the larger side faces greater wind resistance and turns so that the smaller side faces into the wind. Wind direction is determined by where it is coming from. Therefore, if a weathervane is pointing south, the wind is coming out of the south and is therefore a Southerly wind.
How Do Weathervanes Predict the Weather?
Beyond that, the winds also helped farmers predict changes in the weather. With an understanding of local geography, the winds provide fairly reliable information. For example, in the Western United States, the following information generally applies:
West winds generally bring fair skies
Easterly winds usually bring storms
In California, northeast or east winds during the summer or autumn are hot, dry winds that can be gusty and strong
During the winter, north winds warn that stormy weather is approaching, possibly bringing snow
Southerly winds usually bring warmth, humidity and rain (sometimes gentle, sometimes torrential)