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Let’s face it. Long-range forecasts can be hit or miss and the further into the future you go, the more you’re left guessing what weather you’re going to get.
In general, forecast reliability is often met with a high level of scepticism. Meteorologists are likened to baseball players, where batting .300 can get you to the major leagues.
But how accurate are forecasts really? What wizardry is behind professionally predicting the future?
Forecasts come down to math
Although forecasting can be an art, it does begin with hard data.
Stephen Kerr, manager of training and development at Environment and Climate Change Canada, says in order to see what’s coming in the weather, you first have to examine what is happening now.
“A meteorologist essentially follows a process called an analysis, diagnosis and prognosis,” Kerr says.
They first look at radar, airport reports of weather conditions like temperature, wind and pressure, even data captured by weather balloons to get a grasp on how the atmosphere is behaving.
During the diagnosis phase they turn all those reports into a weather story of the day.
“They look at this data and then they really make a clear picture as to what’s occurring,” Kerr says.
“What’s driving it? Then at that point, the meteorologists can start looking into the prognosis, thinking about the evolution of how the weather will unfold by using their scientific knowledge.”
The prognosis stage is where mathematics comes into play.
Meteorologists analyze numerical weather models. These use equations to predict what will happen using the current conditions.
These computer models will show an evolution of pressure, wind, temperature and other atmospheric phenomena over a set period of time. Some models will intricately show the next day or two, others will extend further in time, sometimes up to 10 days or more.
Meteorologists will be able to interpret these models in order to create those forecasts we see on our phones and computers.
Forecasts are not created equal
Now we get back to “the forecast is always wrong” debate. Despite popular belief, forecasts are not created equal when it comes to accuracy.
Believe it or not, the next day or even two-day forecasts are fairly accurate. They may miss a little but meteorologists have a pretty high confidence in what will happen. Once you get further down the road that confidence begins to drop off.
Kerr says the atmosphere’s behaviour is partly to blame. He says some scientists refer to the atmosphere as a chaotic system.
“There’s many processes taking place in the atmosphere which are important to the evolution of the weather.
“And so we’re good at measuring what’s happening in real time and close to real time. I’m talking within the first three days of the forecast.”
“But when you go to seven days, the weather has had a week to evolve in a manner that’s generally more difficult to predict.”
Despite that, Kerr says, through the decades longer-term forecasts have been improving. And they remain crucial, especially when forecasting severe weather events.
Meteorologists look for signals in the forecast model that can alert them of severe weather on the way.
“We could be looking at numerical weather data that shows areas on a map where we might have a high concentration rain forecast over a certain time period,” Kerr says.
“Meteorologists will be able to look at those things that stand out at the end of the forecast period and judge if it makes sense.
“And then if it does, we can convey a message to people who need to take measures to avoid or to mitigate the effects of disaster, say, due to flooding in this example.”
And when those events happen, Kerr says, the responsibility for official warnings will always lie with the meteorologists themselves.
“Alerts are composed and sent by Environment and Climate Change Canada meteorologists to the Canadian public to allow them to take timely measures to avert the loss of property or life due to weather.”
Our planet is changing. So is our journalism. This story is part of a CBC News initiative entitled Our Changing Planet to show and explain the effects of climate change and what is being done about it.