Forecasting snow in Metro Vancouver among the 'most complicated' predictions in Canada
Credit to Author: Kevin Griffin| Date: Fri, 17 Jan 2020 21:52:50 +0000
Forecasting snow meant high stress levels last week for meteorologists at Environment Canada.
They know first hand the difficulties of forecasting in a region where snow arrives like an unwelcome visitor.
“Snow is definitely the most contentious forecast we issue,” said Matt MacDonald, warning preparedness meteorologist at Environment Canada’s Pacific Storm Prediction Centre in downtown Vancouver. “When we issue a snowfall warning, I can tell you that the finger of every meteorologist here is almost shaking when you hit the transmit button.”
One of the reasons for the anxiety is the unique characteristics of Metro Vancouver. The proximity of the ocean and mountains, where warmer weather systems from the Pacific Ocean meet colder Arctic air from the interior, makes forecasting snow and the amount of snow especially challenging.
Matt MacDonald, warning preparedness meteorologist, consults computer models at Environment Canada’s offices in downtown Vancouver.
“I’m pretty confident in saying that forecasting snow for the Lower Mainland is one of the most complicated forecasts in Canada,” MacDonald said.
Mark Madryga, meteorologist for Global News B.C., agreed about the challenges of forecasting snow.
“If you’re close to the water, like downtown or in Tsawwassen or Richmond at sea level, it may be plus 2. When precipitation arrives, it will be more rain than snow, maybe a little snow mixed in,” he said.
“If you’re in areas away from the water, where it’s a little cooler, it may be zero degrees so it may fall primarily as snow or more snow than rain and accumulate more.”
Among broadcasters who forecast weather, Madryga is unusual for being a trained meteorologist. He worked for Environment Canada for 21 years and describes its forecasts as the “best in the business” which he consults before making his own.
Elevation, even when it’s minor, is a major variable affecting whether precipitation falls as rain or snow, he said.
Families enjoy a snow day at Kensington Park in Vancouver on Wednesday as the Lower Mainland was hit by a major storm.
“When I leave the TV station here in Burnaby, sometimes I go up (nearby) Cariboo Hill, which is not a very long hill,” he said. “It’s enough so that it can be rain at the station here at Global and snow just that little climb up Cariboo.”
Madryga said when he gives a forecast that ranges from no snow to 15 centimetres, he’s describing the reality of forecasting in Metro Vancouver.
“Viewers probably think: ‘Anybody can say that, Mark.’ But that’s what’s happening. Downtown or Tsawwassen will get nothing because it’s too mild and close to sea level but Guildford, Metrotown, Langley could get 15.”
Forecasters were much more confident about Wednesday’s snow forecast because several days of Arctic sub-zero weather allowed snow to accumulate on already frozen ground. But those conditions tend to be rare in Metro Vancouver, Madryga said.
“I’d say 80 per cent of the time, ballpark figure, we’re always struggling with that temperature near or a little above freezing,” he said.
Often it’s his snow forecasts that result in ribbing from the public.
“Someone may say, ‘Hey, I thought it was going to snow last night. How come you guys blew it?’
“I’ll say: ‘Wait a minute. It may not have snowed at your place but 10 centimetres fell just up the hill.’
“I get a little defensive and throw it back at them. It’s all in fun.”
At Environment and Climate Change Canada, weather forecasting for B.C., Yukon, and coastal waters is done by a team of meteorologists in a building on Burrard Street.
Their analysis includes using pencils to draw isobar lines, which mark places of equal barometric pressure, on maps of the northeast Pacific Ocean and B.C. on average at least once every six hours.
They don’t use pencils out of nostalgia. Using their hands to draw forces the meteorologists to take into account real-world weather observations and compare them to what models are saying in a part of the world where there are so few weather stations that it’s been called the Pacific data void.
“It’s a great exercise to ground the model’s forecast in what we’re seeing in reality,” he said.
The weather analysis, which also looks at other data such as satellite and imagery, is meant to “paint what we think is the most accurate, current picture of reality,” said MacDonald.
Diagnosis is the next step, where meteorologists look for patterns and ask questions that include: “Is this a cold front? Warm front? How deep is it? Where is it going?”
Meteorologists develop a forecast based on computer weather models.
In Canada, weather modelling is done on computers at the Canadian Meteorological Centre in Dorval, a suburb of Montreal. Its supercomputers are the fastest operated by the federal government and can perform 2,444 trillion calculations a second.
The supercomputers allow the centre to run five different, three-dimensional weather forecast models that take into account variables such as temperature, wind, humidity, air pressure and cloud cover. The highest-resolution model divides the atmosphere into 2.5-kilometre cubes. (An experimental model is down to one-km cubes.)
MacDonald said one of the skills a meteorologist develops is to know under which conditions one model works better than others.
“Working with models we develop rules of thumb,” he said. “Some models have a wet bias or a cold bias, so we’ll tone down precipitation or increase temperature.”
One of the variables the models aren’t yet capable of fully taking into account is diabatic cooling, which occurs when precipitation intensifies and cools the atmosphere.
If the temperature drops to –0.05ºC, rain can start turning into snow. If the precipitation intensifies, it can cause cooling that leads to temperatures dropping further below zero and more snow accumulating.
Lower Mainland residents, including this Coquitlam woman, woke Wednesday to snowy conditions, making travelling treacherous. Many people found it impossible to make it to work.
At the Vancouver weather centre, a meteorologist has developed algorithms to more accurately take into account local diabatic cooling, which is exactly what occurred with the snow on Friday, Jan. 10, he said.
Another big variable is the snow-to-water ratio.
At close to freezing, 10 millimetres of water in the atmosphere may become the equivalent of 10 centimetres of snow. If it’s a bit warmer, the same amount of water might produce only seven cm of wet snow; a little colder and the same 10 mm of water might produce 12 to 14 cm of fluffier snow.
“Converting water in the atmosphere into how much is going to fall on the ground is still one of the trickiest things we do,” he said. “We miss a lot of forecasts simply due to that single variable.”
MacDonald recognizes that forecasting snow is unique. If a forecast 50 mm of rain results in only 30 mm, people often only notice that it rained a lot, not that the forecast was off by nearly half.
“It’s not visual. You can’t see the evidence,” he said. “If you forecast 10 cm of snow, and it snows 40 cm, it’s in your face. You see it and everyone is complaining about it.”
MacDonald is aware of the social side of meteorology. At parties, for example, he often tells his wife not to let anyone know that he works as a weather forecaster. “I’ve heard them all: ‘You’re the guy who gets paid to lie to people’ and ‘You’re the one who can always be wrong and not lose his job.’”
He gets it on the home front, too. “My mother-in-law tells me what the weather will be all the time because she watches The Weather Channel,” he said. “She says ‘Oh Matt, just so you know, there’s a big snowstorm coming.’
“I just smile and nod and say: ‘Thanks for telling me.’”
• In a single storm in Vancouver: 43 cm, Jan. 19, 1935.
• Highest amount on the ground, Vancouver: 61 cm, Jan. 18, 1968.
• In a 24-hour period in Chilliwack: 68 cm Nov. 16-17, 1996.
• In a day in Canada: 145 cm on Feb. 11, 1999 in Tahtsa Lake, east of Kitimat.
• In a season: 2,447 cm at Mount Copeland near Revelstoke, 1971-72.
• In a day in the world: 192 cm – almost two metres – in 24-hours in Silver Lake, Colorado, April 14 and 15, 1921.
• In a year: 3,110.2 cm (31 metres), Feb. 19, 1971 to Feb. 18, 1972, Mount Rainier National Park in Washington state, 1998-99.
— Sources include The Vancouver Sun and Environment Canada