You’re about to run out the door and your phone says there’s a 16% chance of rain. You may be tempted to leave your umbrella at home, but that’s not necessarily the case. Meteorologists use the equation P = C x A, where C is the confidence that rain will fall somewhere, A is the percent of the city or county that will experience rain, and P is the resulting probability of precipitation. To calculate, you multiply C and A and then move the decimal point two places to the left.
For example, if a forecaster is 80% certain that rain will fall but they only expect it to cover 20% of the forecast area, then they would say that there’s a 16% chance of rain for that area. So the 16% chance may be accurate for you, but if it starts raining buckets elsewhere, you now know why. This system isn’t perfect, but it gives forecasters a quick and dirty way to give people a prediction, and one more reason to get mad at weather people.