Definition
A weather rule stating that in the Northern Hemisphere, if you stand with your back to the wind, the area of low atmospheric pressure will be on your left and the area of high pressure will be on your right. In the Southern Hemisphere, the relationship is reversed.
Plain English
A simple way to find where the low and high pressure areas are. Stand with the wind blowing on your back. In the Northern Hemisphere, low pressure is on your left and high pressure is on your right.
Context Anchor
Seen in aviation weather study, surface wind discussions, and explanations of how winds move around high- and low-pressure areas.
Derivation
Named after Christophorus Buys Ballot, a Dutch meteorologist who described this relationship between wind direction and pressure systems in 1857. Knowing the name belongs to a person, not a technical term, prevents the reader from trying to decode 'buys ballot' as if it had a literal meaning.
Why Pilots Care
It lets pilots quickly picture where low-pressure systems lie relative to observed wind, aiding route selection and turbulence avoidance.
Grounding Statement
If you are in the Northern Hemisphere and the wind is hitting your back, lower pressure is on your left side.
Intuition Check
Do not read “law” here as an aviation regulation. It means a reliable weather rule about wind direction and pressure.
Example Sentence 1
Using Buys Ballot's Law, the pilot turned her back to the wind and confirmed the low-pressure system was off to her left, just as the surface chart showed.
Example Sentence 2
In the Southern Hemisphere, the crew used Buys Ballot's Law to expect the low to the right when facing into the wind.