Ontario spring ride will bring thunderstorms, rain and snow

Southern Ontario will see a warm spell with increased thunderstorm risk and possible heavy rain early this week, while cooler air and some snowfall are expected in parts of northern Ontario later in the week.

Southern Ontario is entering a changeable stretch of spring weather this week. A light southerly flow will push temperatures above seasonal in places, while an upper wave and surface low increase the chance of thunderstorms. Heavier rainfall is possible in multiple rounds of convection in parts of southern Ontario. Colder air and a cold front will move in midweek, with snow possible well to the north. Forecast details: - Temperatures may reach the low 20s Celsius in extreme southwestern Ontario (Sarnia, Windsor) and upper teens near the Niagara Escarpment with gusty westerly winds. - Thunderstorm risk rises Monday night and again early and late Tuesday as an upper wave and a surface low move through the region. - Primary threats with storms are gusty winds, small hail and locally heavy rain; 30–50 mm is possible where multiple rounds occur, with the Niagara Peninsula to London showing a higher signal (locally 50+ mm). - Locally heavy rain could lead to ponding and affect Tuesday evening commute corridors across southern Ontario. - Snowfall threat with this system is focused well north, affecting areas such as Timmins and Kapuskasing, and temperatures are expected to fall back to seasonal or below along and north of Highway 401 after the cold front. - A system tracking south of the region late Thursday into Friday could bring showers or mixed precipitation, and a strong low over the Great Lakes during Easter weekend may briefly raise temperatures before another cold front returns cooler conditions. Summary: Changeable conditions are expected through early April, with alternating warmer spells, thunderstorms and cooler periods. The most immediate impacts are gusty winds, small hail and localized heavy rainfall in parts of southern Ontario, while snow risk remains primarily in northern areas. Forecasters will monitor late-week and Easter weekend systems for additional rain, wind and a return to colder conditions.