Your Area’s Chance of Rain Doesn’t Mean What You Think

You might check the weather forecast to see if you need to grab an umbrella or put on a jacket on the way out the door. But you might be interpreting one pretty important part of the weather forecast wrong.

The percentage of precipitation doesn’t indicate your chances of rain. It’s an estimate that involves both the confidence that it will rain and the area in which it’ll rain.

If you’re like me, you always believed that a 60% chance of rain meant that there’s, well, a 60% out of 100% chance that it’ll rain. But that’s not actually the case. Things are a bit more complicated than that. In fact, not even all meteorologists agree. But in general, it all comes down to a little bit of math.

Your probability of precipitation measure is the percentage of confidence it will rain and the percentage of an area that will get it. If you’ve got a 50% confidence rate that it will rain and 60% of an area will see it, you’ve got a 30% chance of precipitation overall. Honestly, it’s pretty complicated and best left to the professionals, but where does this leave you when planning for events and outings?

Honestly, this bit of meteorological knowledge is more of a fun trivia fact than something you might actually use. For the most part, using the percentages you see on your weather app in the way you always have is still going to let you determine your risk of rain. Sure, it’s not a precise understanding of the forecast, but it’s good enough to decide whether you should be going to the park or having a cozy picnic indoors.

But if you happen to be a weather nerd or are always looking to get the next question on Jeopardy right, it’s a fun fact to know.