Open a new browser tab and check your favorite weather forecast website or app. Right now.

How many days in the future does it go? Seven? Maybe even 10? Look at the current forecast for the 7th day out from today. Do you trust it to accurately predict the weather for that day? Why? Or why not?

Have you ever wondered why they can’t just extend the forecast to a full month? Or maybe even 6 months? Wouldn’t that be way more useful than a 7-day forecast in planning your wedding reception, vacation, or family reunion?

But it doesn’t work.  Predicting the weather accurately beyond a week is impossible. Why?

Well, in the 1960s, an MIT meteorology professor named Ed Lorenz, while working on computer models of weather, realized that teeny tiny, almost immeasurably small differences in the numbers he input into his computer ended up significantly changing the long-term weather patterns. Or put another way, his findings suggested that a butterfly flapping its wings in Brazil could cause a tornado in Texas.

This extreme sensitivity of the weather to initial conditions has been termed the butterfly effect. The butterfly effect is why we can’t predict weather accurately beyond a very short time. And, as it turns out, the principles of the butterfly effect apply in all kinds of other areas — from economics to engineering.

via What chaos theory has to do with family medicine.