What 80% chance of rain really means as people ‘highly concerned’ by BBC post

You’d be surprised as many people have said they’re “genuinely worried”

If you’ve ever checked the weather app and it says that there’s a chance of rain, you might think you know what it means. But do you really?

In a BBC video, it’s explained what an 80% chance of rain actually means. While many people assume it’s obvious, there are still some who don’t fully understand it.

For example, there is a dedicated Reddit thread to this exact question. There’s also a Facebook post that shows people “just learning” this fact, with some people thinking it actually means “there will be rain over 20% of the area.”

But this is false. Ben Rich, a BBC Weather Presenter, explained: “If it says 80% that doesn’t mean it’s going to rain 80% of the time or across 80% of your town or city.

“It simply means that if this exact weather situation happened, a hundred times, on 80 of those occasions, it would rain. So it’s probably worth grabbing a brolly.

“On the other hand, if it said 20% it should only rain on 20 out of 100 similar occasions. So you’re most likely, but not certain, to stay dry.”

In the comments, people didn’t hold back. One person thought: “Highly concerned about their need to make this video.” Another wrote: “I was less confused before the video” while a third commented: “It’s very worrying that you needed to explain this.”

In a seperate article updated in September 2025, the BBC weather experts explain: “The probabilities are given for the location chosen, and thus are valid for that location only. As MeteoGroup forecasts take advantage of hourly updates, which include real-time information from radar, satellite, and nearby weather station observations, you may notice the probabilities changing in the short-term (next 2-3 hours).

“This gives you the chance to spot when, for example, a shower may be approaching your location, as the probabilities will tend to rise.”

Why does the weather forecast keep changing?

If you notice that the weather app keeps changing, the BBC article further explains: “Working with our weather data provider MeteoGroup, we provide hourly forecasts out to 14 days.

“When producing forecasts beyond the next few days, MeteoGroup uses weather model information which tends more towards trends in the weather, rather than a single “deterministic” output. Small changes in conditions now can have a cumulative effect and create dramatic changes in the weather several days away, so the forecast further ahead can change considerably.

“Therefore, confidence in the forecast decreases as you move further into the future. However, we believe our audiences understand that and would rather have the information, to give them the ability to see the trends over time to help them make the decisions they need to make.”