Residents of Sarnia, Ontario, should prepare for a significant swing in temperatures and weather conditions as a warm Friday gives way to a much cooler weekend. According to Environment Canada, the city is experiencing an unseasonably warm day today, April 3, 2026, with a high of 23°C. This temperature is significantly above the seasonal normal, providing a brief departure from the cooler, sluggish spring that The Weather Network had initially projected for the province.
While Friday brings warmth, the conditions will shift quickly. Morning showers and a risk of thunderstorms are expected to clear out by midday, but the reprieve will be short-lived. By Saturday, April 4, residents should expect significant rainfall between 10 and 20 mm, accompanied by a risk of thunderstorms.
The weather will become much colder following Saturday’s rain. Temperatures are forecasted to drop to a high of only 6°C on Sunday, with overnight lows dipping to -2°C. This cooling trend continues into early next week, with Monday and Tuesday seeing highs of 4°C and 2°C, respectively, and nighttime lows dropping as far as -3°C.
Observations recorded at the Sarnia Chris Hadfield Airport show how quickly these conditions can change, with early morning reports today already showing mild temperatures of 15°C amid light rain. As the region moves through this rollercoaster of weather, residents are encouraged to dress in layers to stay comfortable as the warm morning air transitions into much colder temperatures throughout the coming days.
Looking further ahead, the forecast suggests a return to warmer conditions mid-week, with temperatures expected to reach 8°C on Wednesday and 14°C by Thursday, though more showers are anticipated to arrive by that time.
