Buys Ballot's Law

In 1857, a Dutch meteorologist named Buys Ballot discovered what we now know as Buys Ballot's Law: In the Northern Hemisphere, if you stand outside with the wind at your back, high pressure is on your right and low pressure is on your left.

Assignment 1: Twists and Turns

1. Try to figure out where high and low pressure centers are from your own back yard, using Buys Ballot’s law. Stand with the wind at your back. Hold your arms outstretched. Which direction is your right hand pointing? That’s the direction to high pressure and (usually) sunny skies. Which way is your left hand pointing? From that direction you will probably see increasing clouds and stormy weather. Check a current weather map for your area, either in the newspaper or online, and see if your backyard observations match up.
2. You can also try to predict the prevailing wind direction in your neighborhood even before stepping outside. While drinking your morning coffee, look at a national weather map. There’s probably a big H for high pressure or L for low pressure stamped somewhere on the page near your home state. With your finger, trace a counterclockwise swirl around the L (or a clockwise swirl around the H). In which direction is your finger moving when you cross over your own town or county? If your finger is moving from north to south on the map, chances are the prevailing wind outside is northerly -- and chilly!

Wind direction always refers to the direction the wind is blowing from, not the direction it’s blowing to. So a northwest wind blows from the northwest to the southeast