It's no secret that spring can be a tumultuous time for Canadian weather, and as an unseasonably mild El Nino winter gives way to summer, there's bound to be a few swings in temperature that seem out of the ordinary.

From Ontario to the Atlantic, though, this week is about to feel a little erratic.

Forecasts show that as a mix of weather systems drifts east from the Prairies in the coming days, Ontarians can expect to vacillate between temperatures as low as below freezing to well into the 20s.

Meanwhile, parts of Newfoundland and Labrador could see freezing rain and snow this week, as the leading edge of the system brings storms across Atlantic Canada.

As of Wednesday, Environment Canada has issued freezing rain alerts along the east coast from Great Harbour Deep, Newfoundland, north to Cape Porcupine, Labrador. Further north, in the Postville and Makkovik area, a blowing snow advisory is in effect.

As for Ontario, Toronto and regions of Niagara and Windsor-Essex-Chatham-Kent are all under frost advisories overnight Wednesday into Thursday morning, warning residents to protect their frost-sensitive plants and trees. By the weekend, temperatures are primed to rise steeply, with Windsor and Toronto at 24 and 22 degrees, respectively, on Sunday.

"It's a bit of a complicated pattern; we've got a lot going on," said Jennifer Smith of the Meteorological Service of Canada in an interview with CTVNews.ca on Wednesday. "[As is] typical with weather, all of these things are related."

Smith said the peculiar mix of conditions can be linked to a low-pressure system that has churned over Hudson's Bay for weeks, pushing colder temperatures south and east into Ontario and Quebec.

At the edge of that cold patch is a jet stream that is expected to bring storms that will dump significant precipitation onto Newfoundland and Labrador. As the cooler air drifts east into the weekend, the warmer air in the Prairies is expected to spread across southern Ontario.

But as varied as the conditions may sound, Smith notes that it shouldn't be taken as especially strange for the season.

"This is just business as usual," she said. "It's a very changeable time of year … we are seeing active weather, followed by cool spells and warm spells, in alternation … spring is quite active, like that."

El Nino weakening

This spring follows an unseasonably warm winter, in which the irregular meteorological phenomenon known as El Nino caused regular patterns of cold weather to be blunted, if not disrupted entirely.

In fact, the 2023-24 season marked one of the most pronounced impacts of El Nino on record, according to the World Meteorological Organization [WMO].

But as the months have drawn on, experts say that the El Nino period, which can often last up to 12 months, has passed its peak.

"It is now gradually weakening but it will continue to impact the global climate in the coming months," reads a March update from the WMO. "Above normal temperatures are predicted over almost all land areas between March and May."

The organization notes that El Nino has a 60 per cent chance of persisting through May, but that between April and June, there is a four-in-five likelihood that the world's weather cycle will transition to more neutral conditions. WMO predicts a possible shift later this year to La Nina, an opposite phenomenon that drives colder temperatures in much of the world.

Smith says that when it comes to these kinds of patterns, it can be difficult to make concrete predictions.

"It's tough to say how that's going to impact Canada going forward through the spring season," she said. "There's a lot that we don't know yet."

With files from Megan DeLaire