Buys Ballot Law

We were going over the Buys Ballot Law in class about a month ago, and it is a pretty neat thing in the weather world! So, what exactly is the Buys Ballot Law?

The Buys Ballot Law simply states that if the wind is at your back (in the Northern Hemisphere), air pressure will be lower to your left. So let’s take a look at a simple example of this using a surface map.

Some things to note before we dive into this: the numbers I have circled for you depict the mean sea level pressure, which is just an indicator of the pressure at the surface. The red arrows show the direction the wind is coming from. For the sake of this example, we will assume the wind is always at your back. The black arrows indicate which direction is to the left if the wind is at your back.

So, let’s say you’re in Bowling Green, notice the wind at your back is out of the south-southeast. If you were to look directly to the left, you would be looking in the direction of lower pressure (the center of low pressure for this example is in southern Illinois, northwest Kentucky, and southern Indiana).

Now, pretend you’re in central Illinois. The wind is hitting your back from the north-northeast. If you were to look to your left, in this example, east, there is lower pressure than to the west, your right. And, if you’re in southeast Missouri, the wind to your back is from the northwest. In which case, the direction northeast is to your left, which is where the lower pressure is.

So that sums up a majority of the Buys Ballot Law! If you’re ever out and about with some friends, and the wind is to your back, blow their minds by telling them lower pressure is to your left.