What You Need To Know About The 'PoP' In A Weather Forecast

DENVER (CBS4) - It's a question we sometimes get multiple times each day in Colorado's Weather Center; what is today's chance for rain?

The answer is called a PoP, or probability of precipitation, which is typically expressed as a percent in the weather forecast.

But what does that number really mean?

If today's chance for rain is 40 percent, does that mean it will rain 40 percent of the time or over 40 percent of the area?

The answer is neither.

A 40 percent chance of rain means there is a 40 percent chance that precipitation will fall at any one point in the forecast area.

BUT WHAT IF NUMBERS AREN'T USED

Depending on what best tells the daily weather story, sometimes forecasters will use phrases like "chance of showers" or "scattered storms" to describe the forecast.

These words can be associated with a PoP.

• 0-20% includes "slight chance" and "widely scattered"

• 30-50% includes "chance" and "scattered"

• 60-70% includes "likely" and "numerous"

• 80-100% includes definitive types of precipitation such as rain, snow or showers

One challenge in understanding what a PoP means for your area is not knowing the size of the forecast zone.

When you see forecast graphics on CBS4 such as the 5-Day Forecast, the PoP's shown are for the area covering metro Denver and the adjacent I-25 urban corridor, which is where over 80 percent of our viewers live.

So in the example above there would be a 20 percent chance that any one spot in the forecast zone will see a thunderstorm on Friday.

For those living or traveling outside of metro Denver we have two different tools for you to find out what the 'PoP' is where you live.

You can click here to access the main weather page on CBSDenver.com and enter your zip code for a detailed forecast.

If you're on the go you can download our FREE CBSDenver Weather App to get forecast information for your area.

Meteorologist Chris Spears writes about stories related to weather and climate in Colorado. Check out his bio or follow him on Twitter @ChrisCBS4.