People get confused about what percentage of rain means on different weather apps

Ever look at your weather app on your phone and wonder how they figure out what the percentage chance of rain is going to be?

If I look at multiple weather apps one of them tells me there's going to be a 75 percent chance of rain in my area tomorrow, but when I get the hour-by-hour breakdown that percentage doesn't go above 50 anywhere.

But if I look elsewhere I get different figures for the same area, with the Met Office and BBC both giving me 80 percent at different times of the day.

So what am I supposed to do with this information?

Obviously I'd better take my umbrella with me when I go out but all these different figures might leave me wondering what I can expect.

Jason Weber/Getty

If you're looking at the BBC's weather app for example and it's telling you there's a 20 percent chance of rain it's because out of 100 simulations with similar weather it's rained 20 of those times.

So on that app it really is the percentage chance of rain based off estimates of past weather conditions.

Even though they're telling me slightly different things about tomorrow's weather it's the same for the Met Office app, it's telling you the percentage chance of rain 'occurring at any one place in the region'.

It doesn't mean that a certain percent of the area will be rained on or that it'll be raining for that portion of time.

It's about the chances of someone living in that specific location getting rained on at a certain time.

Apple

While the UK forecasts generally stick to just the chance of rain in a location things are a bit different in the US.

Across the pond in the US the percentage figure is achieved by calculating the chance of rain and the coverage of the rain in the location the forecast is focusing on.

So if there's a 50 percent chance of rain and it's forecast to cover 80 percent of an area that'd give you a total of 40 percent.

Still with us so far? Good.

What your percentage figure will never tell you is how long your rainfall is going to last or how intense it'll be.

On top of that predicting the weather is just a difficult thing to do in general and rain is especially hard to forecast, if the time or location of precipitation is even a little bit different then it'll throw things off.

Topics: UK News, US News, Weather, Technology

Joe Harker

Joe graduated from the University of Salford with a degree in Journalism and worked for Reach before joining the LADbible Group. When not writing he enjoys the nerdier things in life like painting wargaming miniatures and chatting with other nerds on the internet. He's also spent a few years coaching fencing. Contact him via [email protected]

@MrJoeHarker