Environment Canada has issued a heat warning for the St. Catharines and Grimsby area, with temperatures expected to feel like the low 40s through at least Wednesday. The warning, in effect as of Monday afternoon, flags a stretch of hot and humid weather that could make outdoor activities risky without proper precautions.
Tuesday is forecast to be the hottest day, with the mercury hitting 35 C and humidity pushing it to a sweltering 43. On Monday, the high was 31 C with a humidex of 38, offering little relief overnight as lows dip only to 22 or 23 C. The UV index will sit at 9, which Environment Canada rates as very high, meaning sunscreen, hats, and shade are musts.
The heat is well above normal for mid-July. Typically, Grimsby sees daytime highs around 26 C and nighttime lows near 17 C, making this stretch about 5 to 9 degrees hotter during the day and 3 to 6 degrees warmer at night. The prolonged warmth and sticky nights are what triggered the warning, as Ontario’s rules kick in when humidex values top 40 or when daytime highs of 31 C and nighttime lows of 20 C last two or more days.
Niagara Region Public Health is reminding residents that everyone is at risk during a heat event, though older adults, infants, and those with chronic illnesses are more vulnerable. The region does not issue its own warnings but relies on Environment Canada alerts and points people to public cooling spaces. Libraries and community centres across Grimsby and nearby towns are open for anyone who needs a break from the heat.
Air quality could also take a hit. Environment Canada warned that the hot, humid air mass may push the Air Quality Health Index toward the high-risk category, adding extra strain for people with breathing issues. A change is expected by Wednesday, bringing a mix of sun and cloud along with a 30 percent chance of showers and a high of 32 C. The heat warning could end either Wednesday or Thursday evening, depending on how quickly conditions ease.
