Here's What Your Weather App's 'Chance Of Rain' Percentage Actually Means
There's no shortage of great weather apps available for both iPhone and Android. Most of them are pretty reliable and can provide detailed forecasts for your area and even cities around the world. While much of this data is easy to understand, some aspects can be confusing. For instance, if it's June and you're planning to go out, you'll likely check the weather app to see if it's going to rain. When you do, you might see a 10%, 40%, or even 80% chance of rain. But what does this percentage actually mean?
It's easy to get confused by the "chance of rain" or "probability of precipitation" value. In a viral 2021 TikTok post, a user claimed that a 30% chance of rain means 30% of the forecasted area will definitely receive rain. However, this interpretation is incorrect. Below, we'll explain what the chance of rain percentage in your weather app actually means and how it is calculated.
What does the 'Chance Of Rain' percentage tell you?
The "chance of rain" percentage represents the probability of at least 0.01 inches (or 0.254 mm) of rainfall occurring within the specified period, multiplied by the percentage of the forecasted area expected to receive rain. So, if your weather app shows a 30% chance of rain, it means there is a 30% likelihood (roughly one in three) that at least 0.01 inches of rain will fall at that time and location. This also implies there is a 70% chance of dry weather.
Note that if the weather app shows a 100% chance of rain during a particular timeframe, it doesn't necessarily mean it will rain the entire time. It could rain for just five minutes at any point within that period, but as long as at least 0.01 inches fall, the forecast remains accurate.
To calculate the actual chance of rain percentage, forecasters use the formula: P (probability of precipitation) = C (confidence of at least 0.01 inches of rain) X A (expected area to receive rainfall). So, for instance, if the forecasters are 20% confident that 60% of the forecasted area will receive rainfall, the probability of precipitation or the chance of rain will be 20% X 60% = 12%.
Weather forecast accuracy has improved significantly in recent years, and it will continue to get better with the help of AI. However, understanding how to interpret these forecasts is essential to making the most of them.