Ontario’s unseasonable late-May cold raises eyebrows
At a time when Ontario is usually warming up toward summer, a surprising cold snap is sending temperatures lower than what was recorded in late December 2024. This week, beginning Wednesday, May 21, 2025, will bring persistent rainfall, blustery winds, and daily highs struggling to exceed 10°C (50°F).
Colder than late December 2024? Yes, really
Several Ontario cities are seeing daytime highs this week lower than those experienced at the end of last December. In Toronto, for example, forecast highs are 11°C on Wednesday, 10°C on Thursday and Friday (51.8°F, 50°F, 50°F)—while on December 29, 2024, Pearson Airport reported a high of 10.3°C (50.5°F). Remarkably, March 2025 saw nine days warmer than 11°C (51.8°F).
Wiarton, Ottawa, London, and Hamilton are all experiencing similarly chilly conditions. In Ottawa, temperatures are struggling to reach the double digits, while Hamilton faces three straight days below 12°C (53.6°F), colder than the 12.7°C (54.9°F) high seen on December 28, 2024.
A stalled weather pattern locks in the chill
The culprit behind this unseasonal cool-down is a stubborn low-pressure system parked over the Great Lakes region, paired with a persistent upper-level trough in the United States and a blocking high in northern Canada. This configuration has forced the jet stream to plunge well south, leaving the system stuck and prolonging the gloomy, damp, and cold pattern.
Persistent rain and gusty winds drench southern Ontario
The first wave of rain is expected to arrive on Wednesday afternoon, with steady showers continuing into Thursday and spilling into Friday, stretching as far north as the cottage country. By Saturday, total rainfall may reach up to 40 mm, similar to the entire May precipitation in 2020 (40 mm) and 2022 (47 mm).
Areas near Lake Erie have the highest chance of embedded thunderstorms in the coming days.
Winds will also intensify: by Wednesday evening, sustained speeds of 30–40 km/h with gusts up to 60–70 km/h are expected, especially along the western end of Lake Ontario. For Toronto and communities close to the shoreline, persistent easterly winds—combined with lake temperatures still hovering around 10–11°C (50–51.8°F)—will keep things feeling especially brisk.
Looking ahead to early June
The silver lining of this rainy spell is that it should prevent any early-season drought. The last time southern Ontario faced a notable drought in May was back in 2021. Temperatures are expected to slowly recover next week, trending toward seasonal norms as June approaches. However, the first week of the month will likely remain changeable, with above-normal warmth potentially developing deeper into the month.
Stay tuned to local weather updates as this May cold spell continues to surprise Ontarians.
