If You See a 40% Chance of Rain, This Is What It Really Means
It looks like a 100% chance of math today.
Even the warmest months can have unexpected showers, and you definitely don’t want to get your patio party rained on. When you open up your weather app, you might see a small percentage that lets you know how likely it is that you’ll see rain. However, the meaning of that number is more complicated than any of us realized.
What Does the Percentage of Rain Mean?
According to a viral take on the internet, the percentage of rain doesn’t predict the chances of rain. Instead, it means a certain percentage of the forecasted area will definitely see rain—so if you see a 40% chance, it means 40% of the forecasted area will see rainfall.
But it’s not quite that simple.
Meteorologists aren’t in agreement on how to measure the Probability of Precipitation, aka that little percentage of rain on your weather app. Some use a formula for it — PoP = C x A, where C stands for confidence and A stands for area. So if there’s a 50% chance of rain in 80% of a given area, your probability of rain becomes 40%.
More commonly, meteorologists measure PoP as the chance of rain at any given point in the area they cover during a certain period of time. This is the definition closest to the official definition from the National Oceanic and Atmospheric Administration (NOAA).
What Does This Mean for Us?
Honestly, it probably doesn’t mean all that much. If you’re planning an outdoor event, you’ll probably prepare the same way no matter how you interpret the percentage. If you see 80%, there’s a good chance you’ll postpone your party, and if it’s 20%, you can probably go ahead with it. It might help to learn the lingo with this handy chart, though!