Calgary (Rural Roots Canada) – You often hear it in every weather forecast or read it in weather reports: percentage of precipitation (POP).

But what does that mean? 

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Meteorologist David Spence understands the confusion when it comes to POP. 

“If you take five people and ask them what they think it means, you’ll get five different answers. Some will say it means 30% of the forecast area. Some will say it means a 30% chance of rain because that’s what it says. But that’s not what it means,” says Spence. 

So, what’s the right answer? 

“What it means is, there is a 30% chance it will rain with a measurable amount at some point in the forecast area during the forecast period.” 

Spence gives the example of a 4 p.m. weather forecast for Airdrie, Cochrane, Olds and Sundre that calls for a 30% chance of rain.

“That’s a very wide area and one forecast zone from Environment Canada…and it doesn’t rain in Airdrie, you think the forecast is wrong. It doesn’t rain in Olds, and you think the forecast is wrong. But Sundre gets one millimetre of rain. So, there’s the rain for that entire zone that happened. A very small amount in a very small area, and that’s why you get a 30% chance of rain forecast for the zone. It doesn’t mean you have a 30% chance of rain at your house,” explains Spence. 

“It just means somewhere in that zone, there’s a slight chance it might rain.”

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For farmers, understanding the weather data, especially during harvest, is vital to make the necessary preparations. Spence recommends a weather website called Spot Weather. You enter your address and, in return, you’ll receive a series of weather models. 

“Weather forecast models take a little bit of work to interpret, but I think the average user can figure it out because there’s a graph that shows rainfall. So, you’ll get graphs showing when it’s going to be cloudy and when it’s going to rain, and you can use that to determine whether rain is likely to fall.” 

While complaining about the weather is a national pastime, understanding weather data and terminology can limit the griping and allow you to be better prepared for the harvest season.