What Does 20 Chance of Rain Mean?

June 1, 2023

There’s been a lot of confusion this summer about what “chance of rain” means on TV and in weather apps. This confusion can be attributed to a viral TikTok video that misrepresented what a chance of rain actually is. Chance of rain, also known as Probability of Precipitation or PoP, is the likelihood that a point in a forecast area will experience measurable precipitation during a certain time period. It’s calculated by multiplying two things: 1) the confidence a forecaster has that rain will happen, and 2) how widespread they expect that rain to be. Let’s say a forecaster has 100% confidence that it will rain and they are expecting 80% of their forecast area to get rain. The chance of rain will be (1 x 0.8), which is equivalent to a 70% chance of rain.

However, chances of rain don’t tell us anything about how much rain will fall or how long it will last. That’s why it’s important to watch for a phrase like “scattered showers” or “patches of rain” in the forecast, as these indicate that it will likely be very light.


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