Updated April forecast: Find out when spring really starts

Friday, April 8, 2016, 9:48 AM - A week ago, as we were analyzing the pattern that has defined the first several days of April we asked the question: “Could April be snowier than December in southern Ontario?”.

The atmosphere gave us an emphatic answer, with multiple rounds of snow impacting southern Ontario and Quebec. This allowed many parts of the region to stack up some impressive springtime snow totals – including 17.7 cm for Toronto and 14.2 cm for Ottawa. Some localized spots were hit even harder, for example Hamilton, Ont., where the official total through April 7 stands at 25.3 centimetres.

Now we have some new questions to ask: Will we see any more threats for snow this month, and will April end up being the snowiest month of the entire “winter” season? Or will eastern Canada finally catch up to the west, and see the arrival of truly spring-like weather in the days ahead?

We have all the details below.

Here’s a look at the current pattern, as we round out the first week of April. A deep trough over Hudson Bay has cold air stuck firmly in place from the eastern Prairies through Ontario and most of Quebec. Meanwhile a persistent ridge has allowed early summer-like warmth to take hold in the west. Atlantic Canada finishes the week on a stormy note, which will bring rain, snow, wind, and a temperature roller coaster ride to the region.

As we move into the weekend, we expect to see a reinforcing shot of cold air, which will make Saturday the coldest day of the period for most of Ontario and Quebec. This will bring widespread temperatures more than ten degrees below seasonal (areas in purple), and threaten to break record lows for places like Toronto on Sunday morning.

This cold air moving aloft will bring back the threat for lake effect snow squalls, and at the same time a clipper system will track through the Ohio valley. Though the system should be weak enough and far enough south to avoid significant impacts for southern Ontario, a couple of centimeters of snow will be possible across the southern part of the region.

Atlantic Canada will see active early spring weather this weekend, as strong ridge building in across the north Atlantic sets up a sharp contrast in air masses. This will push warm air as far north as Greenland, and bring mild temperatures and rain for Newfoundland and Labrador. Along the transition zone, we’re looking out for messy conditions, including a swath of impactful snow which may affect parts of Nova Scotia, PEI, and eastern New Brunswick on Sunday.

As we watch our Atlantic system depart late Sunday, we’ll also be looking for the arrival of the next significant system for Ontario and Quebec. With cold air already in place, precipitation will start as snow across the region before changing over to rain – with the potential for a brief period of ice pellets and freezing rain in between.

The timing will need to be refined as we get closer, but expect wintry precipitation to impact southern Ontario late day Sunday into Sunday night, and the St. Lawrence valley Sunday night through Monday morning. The most significant snow totals from this system will occur far to the north, but a large part of the region will pick up more than five centimeters before switching over to rain.

With this system bringing the likelihood for additional snow accumulation, areas across southern Ontario should easily see April take the top spot as the snowiest month of the 2015-2016 snow season. Toronto Pearson is already just a shade under February’s total as of April 7th, with more snow recorded in April than December and January combined. Though snowy Aprils aren’t uncommon in Toronto, it has been quite a while since we’ve seen numbers like this. The last time Toronto saw more snow in April was 1979, when 25.8 cm fell during the month.

Looking even farther ahead, the major forecast challenge will be to determine if we will see any more threats for snow and cold in the east in the month of April, or if we will begin to transition into the warmer and dryer pattern that we expect to dominate the majority of the mid-to-late spring. There is still significant uncertainty in the forecast this far in advance, but indications are that that during mid-month we should see a return to near-seasonal conditions, meaning that the weekend of April 16-17 is likely to bring more pleasant temperatures for Ontario and Quebec than the frigid weekend we have upcoming. By the latter part of the month, we do expect a warming trend to take hold for good from coast to coast, finally bringing the true arrival of persistent spring-like weather for most of Canada.