Q&A: What is driving Edmonton's recent heavy rainfalls?

When it rains, it pours — or at least it does in Edmonton lately. CBC News spoke with a meteorologist about what's behind the recent intense storms and what precipitation Edmontonians can expect for the rest of the summer.

Q&A: What is driving Edmonton's recent heavy rainfalls? City on pace for record summer rainfall, meteorologist says When it rains, it pours — at least it does in Edmonton lately. Last month was the wettest June on record, with 264 millimetres of rain falling — shattering the previous record of 216 millimetres in June 1914, according to Dan Fulton, an Environment and Climate Change Canada meteorologist.

Edmonton has received about 95 millimetres so far this month, with half of July left to go, he said. "It's an exceedingly wet summer for Edmonton — and I'd say for the southern Prairies, at least as a whole," Fulton told CBC News. Edmonton has recorded almost 360 millimetres of rain so far this summer, so it's nearing the all-time record of the 417 millimetres that fell during Summer 1953, Fulton said.

But instead of rain accumulating over consecutive days, much of the recent precipitation has come during massive downpours. Flooding shuts down parts of Yellowhead Trail for second time in a week: police A look at Edmonton’s plan to curb future flooding Those sudden bursts have flooded streets and buildings across Edmonton. CBC News spoke with Fulton to learn more about why there have been such intense rainfalls, and what Edmontonians can expect for the rest of the summer.

This interview has been edited for length and clarity. What's driving the heavy rainfalls in Edmonton? There are a couple things driving it.

One thing, for sure, is climate change. As the atmosphere gets warmer, it can hold more water. Then, whenever you have a thunderstorm, the amount of water in the atmosphere holds can just dump on you in that spot, if you happen to be under the thunderstorm.

The other thing going on this year is that the jet stream is kind of meandering, which means that weather systems tend to linger around for a few days. So instead of things kind of moving quickly through Alberta — which is more the normal thing — they stick around for days and just produce all this rain. That also means we're able to tap moisture from the south — basically, from America — a little more easily because these systems stick around, and you're getting a more persistent feed of moisture into the area.

How can these storms, even just within a couple of hours, unleash so much rain? It ties into, actually, a couple of things I said earlier. First of all, the storms tend to be slower moving.

In the summer, you do get the odd thunderstorm and it's a heavy rain, but usually moves on pretty quickly. But these ones are sticking around because the flow that kind of pushes them along is very weak this year. The second thing is that the rainfall rate is heavier, because the atmosphere can hold more water.

You're basically lifting all this really humid, moist air up and, under the thunderstorm, that's where you're getting your rainfall rate. So the air that's being forced up, and being made to precipitate, has a lot more water in it, hence you get heavier rainfalls. It's kind of a combination of climate change, which is the warmer atmosphere, and the jet stream breaking down a little bit and not moving the storms on as much as they normally do — which might be a climate change thing too, but that also varies from year to year.

Typically, how long would it take for a thunderstorm to pass through? Is it normal for it to kind of hover over for a few hours? It depends on the time of year.

But I'm going to say in Alberta it's not that normal, because usually they move on at a decent pace. As you get a little bit further east in the Prairies, it becomes a little bit more normal. But usually things are pretty progressive in Alberta.

If things continue at this pace, we might shatter records here. But do we have a sense of what the forecast might be for the rest of the summer? I'm hesitant to give predictions because summer is so variable ...

but I will say, weather tends to kind of follow the precedents that it's been doing. We've been wet and we'll probably continue being wet until, at some point, we get a little bit more established in progressive systems, like the jet stream, moving things across the Prairies — and that usually doesn't happen until fall. So I would not be surprised to see this continue for the remainder of the summer.

With files from Nicholas Frew