What does 'chance of rain' really mean? | Up in the air | Met Office Learn About Weather

Have you ever checked your weather app and wondered what 'chance of rain' or 'probability of precipitation' really means? Does it mean 20% of the area will get wet? Does it mean raindrops will be 20% smaller than usual? Or does it mean something completely different. Watch this video to discover the true meaning of 'chance of rain' so that you have a better understanding of how to interpret your weather app and so that you are better prepared to face whatever the weather has in store from sunshine and showers to rain and snow.
Written and presented by Aidan McGivern
Animation by Drive Creative Studio Ltd
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[@idfitter]

This is interesting as the explanation I was given was that for other days where the measured conditions were the same, it rained on 20% of those days.

[@HGParrot]

So helpful, i saw the tiktok previously and when looking at today's forecast I couldn't remember the calculation @2:57 when looking at a few hours block, I had remembered correctly but it's a really useful video to come back to. Would be great if this information could be added to the forecast on the website either under the i button for chance of precipitation or what does it meant section

[@wellnessgirl2806]

Great explainer thanks ✨😊

[@Kylepittendreigh]

Thanks for this aiden

[@Kylepittendreigh]

Aiden you forgot about thunderstorms can thunderstorms impacts the chances of rain

[@MetOfficeLearnAboutWeather]

Thunderstorms will be covered in next week’s animation!

[@adrianharding4769]

So according to the example given at 3:00, if for a 10 hour period the chance of rain is 5% in each hour (in other words it's a sunny day with very low chance of rain), I should expect to get wet during 40 out of every 100 similar 10 hour periods. That feels wrong. Basically, I'm almost as likely to get wet as not. And that's on a day with no hour having a greater than 5% probability of rain 🤯

[@MetOfficeLearnAboutWeather]

Technically, yes, that is how probability works. Although, admittedly, the video simplifies the complex and often very messy situations that are showery days in the UK. On some days, the formation of showers will lead to the formation of other showers. On other days, showers that form in one location will prevent the formation of showers in another location due because the overhanging cloud or the downdrafts will discourage updrafts. So, of course, it's not as simple as rolling dice. Also, a 5% chance of rain doesn't necessarily translate to a 5% chance you will 'get wet'. It might be two drops of rain from a fleeting and very light shower. Or it might be a very low chance of a torrential thunderstorm. This additional information (chance of a very light shower or torrential thunderstorm) will be reflected in the symbol and / or in the presented forecast.

[@サンゴ礁Scleractinian]

If these probabilities were independent, you would be correct. In practice, these probabilities are unlikely to be independent, so it would depend on the specific forecast.