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What the 'chance of rain' really means, highlighted by viral TikTok video

It's not as simple as the odds it will rain, believe it or not. The percentage often leads to... a 100% chance of confusion.

PORTLAND, Maine — A TikTok user's explanation about the probability of precipitation - or chance of rain - took social media by storm Monday.

"I thought 100% that when they said there's a 30% chance of rain, that it means there was a 30% chance it was going to rain. I never knew it meant 100% it's going to rain, and it's going to be in 30% of your area," the TikTok user shared.

The fact that this quick video about, of all things, a certain part of the weather forecast shows how this concept is probably the most misunderstood thing you see on an app or on TV.  It really just leads to 100% confusion!

So, let's break it down. We calculate this percentage using an equation that takes into account both the areal coverage of the rain - and the certainty in the forecast.

PoP = C x A

Probability of Precipitation = Confidence x Area

C is the confidence the precipitation will occur somewhere in the forecast area, and A is the percent of the area that will receive measurable precipitation.

So, I could be 100% confident that 40% of our area will see rain.

Using the equation, that gives you a straightforward 40% chance of rain.

But what if I think 40% of our area will have rain, but I'm only 50% confident in that forecast?  

Well, doing the math, the chance of rain gets bumped down to 20%.

This is taking into account my lack of confidence that I'm not totally sure that it will rain, but if it does, I think 40% of the area gets it.

Note that this percentage doesn't consider the intensity, amount, or length of time it rains, so understanding whether it's just a chance for a thunderstorm or an all-out rainstorm is important.

There's a reason we don't use these percentages in our NEWS CENTER Maine forecast daily; they are confusing. In the event we do use them, we use them to communicate your risk of getting rain or snow. 

Thanks to TikTok, I'll never forget that this is kind of tricky to understand.