What do daily rain chances really mean?

It may not be what you think

Photo does not have a caption

ORLANDO, Fla. – You see it every day. “There’s a 30% chance for rain Friday and a 30% chance for rain Saturday.” But what do those numbers actually mean?

It doesn’t mean that it will rain 30% of the day. It also doesn’t mean that 30% of the area will see rain. A viral TikTok video of all things got the conversation started earlier this year when a user incorrectly defined the rain chance, also known as the probability of precipitation.

@sydjkell

#stitch with @sooklyn #ColorCustomizer I have toooo many of these. I’ll do another weather one. #embarassing #iwastodayyearsold

♬ original sound - Syd

It doesn’t mean that there is a 100% chance that 30% of the area will see rain as the user states. This is what the actual definition is.

Rain chances defined

If there were a 30% chance for rain on a given day, that means that at any point in a given area for a duration of time, in our case Central Florida, you have a 30%, or 3 out of 10 chance of seeing rain.

Believe it or not, there is a mathematical equation that does take into account areal coverage, but also forecaster confidence.

POP equation

That would be the percentage if a meteorologist is pinpointing for a specific location, say Walt Disney World since the park isn’t going anywhere and the forecast becomes one point that won’t move. The chance would actually increase a little if you were moving around the region.

If all of this is still confusing, which it is, just know that a higher percentage increases your likelihood of getting wet at a set time, whether it be an hour in your Pinpoint Weather app, or for the entire afternoon as a whole.

One more important thing to note: The percentage doesn’t take into account rainfall intensity or duration, so even if rain chances are low, it can still be extremely intense or last a while where it does fall.


About the Author:

Jonathan Kegges joined the News 6 team in June 2019 as the Weekend Morning Meteorologist. Jonathan comes from Roanoke, Virginia where he covered three EF-3 tornadoes and deadly flooding brought on by Hurricanes Florence and Michael.