The Western Star
I love my job and all that goes along with it – meeting you, the weather consumers, explaining the science behind things that happen in the sky and sharing my Grandmother’s wisdom with anyone who will listen.
While the weather is not always enjoyable, I hope my presentations are. I don’t mind when people compare forecasts from different sources; in fact, I encourage it. Some forecasters do a better job with certain weather parameters, some might focus more on your location, etc. It’s always good to shop around.
On Sunday, I was having coffee in bed when I decided to check out a weather app. There it was, the forecast for Dartmouth, N.S., for the day – with a “30-per-cent chance of precipitation”; it was raining outside my window at the time.
The dreaded and misunderstood “probability of precipitation or chance of precipitation…” The POP was implemented by the Weather Bureau (now the National Weather Service) of the United States in 1966. Canada later came onboard with the chance of precipitation.
You might find a forecast that looks like this: a mix of sun and cloud with a 30-per-cent chance of precipitation. What does it mean? Well, for starters, it does not mean…
- There’s a 30-per-cent chance it will rain and a 70-per-cent chance it won’t;
- Three out of 10 times when the weather is similar, it will rain;
- Precipitation will fall 30 per cent of the day (or night);
- Thirty per cent of the forecast area will experience rain, snow, or storms.
In Canada, the correct interpretation is as follows: there is a 30-per-cent chance that 0.2 mm of rain or 0.2 cm of snow will fall on any random point of the forecast region during the forecast period.
Really? If it’s raining – then it’s 100 per cent. That’s how I see it, and that is why you will never find a “percentage chance of rain” in my forecasts.
I prefer to qualify the likelihood of rain or snow with words that describe my confidence in the occurrence and specific location of forecast precipitation.'
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Cindy Day is the chief meteorologist for SaltWire Network.