Why Vancouver isn't Winnipeg: reading Canada's climates

Lytton, British Columbia, on the bench above the place where the Thompson River meets the Fraser. Kevin Spintlum is 52, Nlaka'pamux, born here, and he runs the hardware store in a town that is rebuilding. He points west, at the Coast Mountains. Behind them, he says, Vancouver is drowning in rain. Here it is sunny and dry, and in summer, some years, hotter than anywhere else in the country.

So here's the question. Vancouver and Lytton share the same average temperature over the year. So why is one soaked and the other parched? And why is Winnipeg, at nearly the same latitude as Vancouver, twenty degrees colder in January?

The numbers come from Environment and Climate Change Canada's climate normals, averaged over 1991 to 2020. Vancouver: January 4.1 degrees, annual mean 10.5, and nearly 1,200 millimetres of precipitation, hardly any of it snow. Lytton: January minus 1.1, July 22.6, the same annual mean. Winnipeg: January minus 16.3, July 19.5, and 519 millimetres.

Four things make the map. The ocean: the Pacific keeps Vancouver's winter above freezing. Mountains: wet air rises over the Coast Mountains, rains out on the seaward side and comes down dry on the far side, the rain shadow Lytton sits in. Distance from the sea: Regina swings from bitter cold to summer heat; Regina's extremes run from minus 41.9 to plus 41.3. Latitude: Iqaluit's July averages 8.1.

The Great Lakes add a twist. Cold air crossing open water picks up moisture and drops it as snow downwind. The normals: Toronto's airport gets 115 centimetres of snow a year, Ottawa 232, and St. John's 363, the snowiest and wettest big city. Regina is the driest, at 390 millimetres.

Find it on the map. This is a climate graph, from the Vancouver normals. The line is the average temperature, month by month; the bars are precipitation. First the line: does it stay flat and above zero, like this one, or plunge deep below zero, like Winnipeg's? Then the bars: tall in winter and short in summer means a Pacific coast; tall in summer means the Prairies.

Let's change one fact. Flatten the Coast Mountains. The wet Pacific air would roll straight across British Columbia with nothing to lift it, so it would keep its rain. Vancouver would be drier, Lytton wetter and cooler, and the Okanagan, which grows fruit because it sits in that same dry shadow, would be growing something else. Mountains don't just make scenery. They decide where the rain lands.

The mistake people make is thinking Canada is cold everywhere, all the time. Vancouver's January averages plus 4.1 degrees. Lytton reached 49.6 degrees on the twenty-ninth of June, 2021, the highest temperature ever recorded in Canada, by Environment and Climate Change Canada's count. And Winnipeg's July averages 19.5. Cold is a season and a place, not a country.

Here's the rule, in one breath. Oceans soften, mountains split the rain, distance from the sea makes the swings, and latitude sets the ceiling.

This week, find your own city's 1991 to 2020 normals on the Environment and Climate Change Canada website, and check tonight's forecast against the average for this month. Above or below? By how much? After a week of that, you will know your own climate better than most people who have spent years in it.

Next time, the extremes: Snag at about minus 63, Lytton at 49.6, permafrost under about forty per cent of the land, and what the government's own report says about a warming country.