Yet another TikTok video has gone viral as one creator revealed what a 30% chance of rain really means on your weather app.
Instead of meaning that there is a three in ten chance that it will rain, the TikToker said it means that there is a 100% chance that it will rain, but the rain will only cover 30% of your area.
The TikToker’s reason was soon debunked as the real explanation of what the percentage means was revealed by meteorologists.
The percentage given on weather apps is called the Probability of Precipitation (PoP), and here is where it gets complicated.
Many meteorologists disagree on how the percentage is calculated as there are five different definitions for calculating the PoP.
There are several mentions of the misinterpretations of PoP in academic articles dating back to the 2000s.
Some of these articles use the same method as the TikTok video claiming that a 30% chance of rain refers to the proportion of rain that will cover the given area.
Another suggests that PoP means you will see rain for 30% of the time over a given forecast.
Both of these theories are incorrect, meaning that the viral TikToker was too wrong.
Meteorologists believe that PoP miscommunication occurs because weather apps are lacking a reference class.
Dr Castle Williams, a social science contractor supporting National Oceanic and Atmospheric Administration's Research's Weather Program Office, told Refinery29: "A percentage in a PoP forecast is most useful when the percentage is accompanied by a point of comparison that anchors the intended meaning of the forecast."
"For example, if I say there's a 20% chance of precipitation for your area tomorrow in the afternoon or evening, it's unclear what that 20% is referring to.
“By adding a reference class, such as, on one in five days like today, there will be rain in your area, it provides context and anchors the probability information."
Due to the fact that there are never any major consequences to the misinterpreting of rainfall, there has never been a motive to make people understand how to use PoP properly.
Dr Williams said: “The worst that happens is you don’t bring your umbrella or raincoat.
“We have more dangerous hazards that are taking the stage.”
Meteorologists across the world have become more focused on tracking hurricanes, tsunamis and other weather events that can endanger people lives.
Dr Williams said: “Even though people aren’t understanding or can’t define what the PoP means, they’re using the percentage correctly when they take protective action.”
Chances are, if you see that there is a 90% chance of rain, you will act accordingly and be prepared even if you think, like the TikToker, that it is referring to the amount of land the rain will cover.
