In search of an accurate weather forecast

Canada is a nation obsessed by weather, with farmers and ranchers perhaps the most obsessed of all. Many of us wouldn’t know how to start a conversation if it wasn’t for the weather.

You look at the weather app on your phone and see a prediction for 20 to 25 millimetres of rain on Thursday. Good, you think, the rain is timely and badly needed.

However, your spouse heard on the local radio station that Thursday has only a 60 per cent chance of showers. Meanwhile, your neighbour who subscribes to a farm weather forecast service says the outlook for Thursday calls for no precipitation at all.

Which forecast is most accurate? How are these forecasts even derived?

Big weather models drive forecasts

Some weather services just regurgitate forecast information that mirrors the public system. They don’t necessarily employ any meteorologists.

On the other hand, numerous private weather services such as The Weather Network and World Weather Inc. have their own meteorologists and generate their own forecasts. However, it’s important to note that the basis for their work is the publicly funded weather forecast bodies that employ huge, expensive supercomputers to perform forecast modelling.

The Canadian system is part of Environment and Climate Change Canada. The U.S., European Union and Japan all have their own systems churning out world-wide forecasts. Each monitors what the other is doing and each model has its strengths and weaknesses.

From the publicly available information, meteorologists from private weather firms may add their own interpretations. Sometimes this involves localizing the available information or customizing it to be more user friendly for a particular interest group such as agriculture.

Private firms also have the ability to deviate from the public forecast models, giving greater or lesser weight to specific parameters.

“It’s important to realize that each weather service isn’t re-inventing the wheel,” says Bruce Burnett, director of weather and markets for Glacier FarmMedia. For years, Burnett monitored global weather and markets for the Canadian Wheat Board. “There are a lot of forecasts, but not a lot of clarity of where the information is sourced.”

Andy Nadler of Peak HydroMet Solutions agrees that most people are unaware of how weather forecasts are formulated. “Many private forecasters provide forecasts for a smaller geographic area, but this granular forecast may or may not be more accurate,” says Nadler, who supplies weather and climate-related services to a number of agricultural companies.

Which forecast is best?

Nadler and Burnett also agree that forecasts overall are getting better, but neither can provide a definitive answer on which forecast is the most accurate.

“How do you measure accuracy?” Nadler asks, rhetorically. He notes that forecasts tend to converge as the time draws closer. Forecasters might have widely varying predictions for Day 7 of a seven-day forecast, but they are likely to be in reasonable agreement by the time Day 7 is tomorrow.

“We claim 95 per cent accuracy for Day 1 of our forecast period,” notes meteorologist Terri Lang of Environment and Climate Change Canada. “However, people tend to remember the five per cent when we don’t get it right.”

For the first two days of an Environment Canada forecast, there’s some human element massaging the prediction that comes from the supercomputer modelling. Past two days, the model information without any adjustments forms the forecast.

Lang doesn’t believe there’s a great deal of latitude to improve computer modelling. At some point, extra data just becomes information overload, even for supercomputers. However, she is enthusiastic about the upgrades coming to weather radar stations across the country.

No one can accurately predict the path of summer thunderstorms, but with weather radar everyone can watch thunderstorm development and tracking in real time. It has become a valuable tool for producers and will only get better as new radar stations come on stream. 

Weather radar upgrades

A modernization of Canada’s weather-radar network began this year. According to Environment Canada, the country’s 31 radar stations will be replaced at a rate of four to seven per year.

The new systems will enable forecasters to better distinguish between rain, snow, hail and freezing rain, resulting in more precise and timely weather watches and warnings. The new stations will also have an extended severe-weather detection range.

The radar structure is composed of an open lattice steer tower with a 12-metre diameter radome on top. Total height will vary from one site to another, but could be as high as 40 metres, the equivalent of a 12-storey building.

U.S. precipitation forecast includes Canada

You may have seen colour-coded precipitation forecast maps for North America from the U.S. National Weather Service. They go by the letters QPF, which stands for Quantitative Precipitation Forecast. Five and seven-day forecasts are provided, but just like Canadian forecasts, they aren’t always correct.

To find these forecast maps, just search U.S. QPF.

Seasonal forecasts lack accuracy

Environment Canada and many private forecasters release long-range or seasonal forecasts, but the accuracy remains poor. Long range temperature forecasts have a bit more credibility, but precipitation forecasts are not much better than flipping a coin.

“Too many factors come into play for seasonal forecasts. It makes them really, really challenging,” Lang says.

But that doesn’t deter Canadians from wanting to know the long-range forecasts and then talking about them. 

From an AgriSuccess article (November 2018) by Kevin Hursh.