A complex system pushing through the Great Lakes could set off showers and thunderstorms Tuesday night and Wednesday. The first troublemaker of the unsettled weather will be a warm front ushering in rain and possible embedded thunderstorms through Tuesday overnight. Another round is expected to push in Wednesday morning, possibly setting the stage for a more potent wave of thunderstorms in the late afternoon -- depending on when the initial bout departs and timing of the clearing skies. The severe threat is very conditional. Temperatures will be warm once again Wednesday, but again will remain west of the GTA, where daytime highs will be several degrees cooler because of cold lakes and an onshore flow. More on the thunderstorm threats, plus a look at how we start the month of May, below.
TUESDAY NIGHT: THREAT FOR STORMS WITH WARM FRONT
The warm front that is draped across southern Ontario will bring showers and a chance of embedded thunderstorms through the overnight hours. In any storms that do fire up, the main threats will be small hail and heavy rain.
The showers and thunderstorms may linger into the pre-dawn hours Wednesday morning, but more rounds are expected to develop in the day.
WEDNESDAY: CONDITIONAL RISK FOR STRONGER STORMS
The warmth will creep its way further into southern Ontario Wednesday, with slightly milder air reaching the western end of Lake Ontario. However, that is where it ends as most of the GTA will be several degrees cooler than southwestern areas, thanks to an onshore flow. Daytime highs will soar into the 20s for areas in the southwest once again.
The pleasant daytime highs will be accompanied by multiple rounds of showers and possible thunderstorms, with the first wave trekking through in the mid-morning period. Depending on when the initial bout of precipitation moves out, the region could be looking at a second, more potent round of showers and thunderstorms in the late afternoon and early evening hours.
But the risk is very conditional and two scenarios are possible. The first has cloud cover lingering into the afternoon, limiting the ability of any daytime heating, so any stronger storms that develop will remain south of the border. This will still result in showers and possibly rumbles of thunder as the cold front passes through, however.
The other option that may arise will see clearing occur much sooner in the day, around midday and early afternoon. This will allow instability to build, and as the front crosses, could spark strong, potentially severe thunderstorms by the late afternoon or evening.
The main threats from the storms will be similar to Tuesday night's chances, though could be accompanied by stronger wind gusts.
Rainfall amounts will vary across the region, with higher amounts in thunderstorms. Widespread 5-10 mm is anticipated across the south, with as high as 15-30 mm for a swath of cottage country extending into southeastern sections.
As well, winds will be strong Wednesday, in thunderstorms and after the passage of the cold front in the evening. Gusts of 50-70 km/h are expected, though could be stronger in thunderstorms.
The front will move out in the evening, but that won't be the end of the unsettled weather, with more showers and cooler temperatures expected for Thursday.
LOOK AHEAD: COOLING INTO THE WEEKEND AND FOR THE START OF MAY
By Thursday, temperatures will take a noticeable dive in the southwest after the passage of the front, with cooler daytime highs continuing across the south into the weekend and as we start the month of May.
As well, a system tracking south of the border will bring in another bout of showers to southern Ontario, especially in southwestern sections and the GTA. Friday will see more chilly temperatures and showers as the month comes to a close. Conditions will be fair for Saturday.
A tricky forecast for Sunday with a warm front anticipated to push into the region, depending on how far north it can advance.
"A few days of warmer weather is possible next week, but it looks like this region will struggle to see consistent warmth through early May," says Dr. Doug Gillham, a meteorologist at The Weather Network.
BEWARE OF MIDGES, FORECAST FOR CYCLISTS ACROSS ONTARIO THIS WEEK
Be sure to check back for updates on the spring temperature rollercoaster across southern Ontario as we head into May.