Why the “chance of rain” forecast causes so much confusion

We’re in the business of communicating the weather and what works best isn’t the way we’ve always done it. When a Meteorologist calls for “Pops,” it doesn’t mean that you’re going to enjoy a big gulp of Dr. Pepper!

probability of precipitation (POP), is the measure of a rain chance for a specified forecast period and location. But most people aren’t exactly sure what a POP is.

Some people may think a 30% chance of rain means that 30% of the area is going to rain or that there’s a 30% probability that all locations are going to get wet. Instead, a 30% chance of rain means that any one location has a 3 in 10 chance of seeing rain.

Probability of precipitation isn’t something that’s just thrown around by a Meteorologist. There’s actually a math equation that goes along with it. Meteorologists first have to put a number to the confidence that precipitation will occur somewhere in a coverage area. That number is multiplied by the percentage of area that will see rain.

This gives us the POP. Today, we have about a 60% chance of rain.

But here’s why it’s not the best way to communicate what’s going to happen.

If there’s a 30% chance of rain and three people are getting wet, they may say, “Why is it raining? They said only 30% chance…they are never right!” For the seven people who don’t see rain on that day, they may say “Why isn’t it raining? They said there was a chance today…they are never right!”

Conveying the probability of something is sometimes harder than just putting it in layman’s terms: there’s going to be some rain today, but most of you will stay dry.

While we occasionally use a percent on a graphic or in our weather story, it’s not a big part of what we do. We prefer to use words instead of numbers: isolated, scattered, likely, certain. Those words are in bold, while the percentages are gray, small, and narrow.

We’re in the business of communicating weather. Honestly, probabilities and percentages are not only confusing but hard to remember when you see them laid out across an extended forecast graphic. I just want you to know that this weekend’s rain will begin Friday night and remain scattered for Saturday and Sunday.

-Meteorologist Eric Sorensen

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