A record-shattering heat wave is advancing across the United States and Canada, placing more than 100 million people under extreme heat warnings as temperatures soar to historic highs from the West Coast to the Great Lakes and Northeast. The National Weather Service and Environment Canada have issued alerts stretching from the desert Southwest and northern Plains through the Midwest and into New England, with the most dangerous conditions expected to peak in eastern regions by Wednesday.

In the western United States, multiple all-time temperature records have already fallen. Salt Lake City, Utah, reached 109°F (43°C) on Sunday, surpassing a mark set in 1960, according to the National Weather Service. Billings, Montana, recorded 111°F (44°C), while Miles City, in the same state, hit 115°F (46°C). The heat index — a measure combining temperature and humidity — was forecast to reach 110°F (43°C) across the northern Plains on Tuesday, with Fargo, North Dakota, and Rapid City, South Dakota, both threatening daily records. In Canada, Toronto saw temperatures climb to 36°C, nearing the city’s all-time high, and Environment Canada warned that humidex values in southern Ontario could make it feel as hot as 45°C.

As the high-pressure system responsible for the heat dome shifts eastward, severe thunderstorms are erupting along its periphery. The US Storm Prediction Center has flagged an enhanced risk of damaging winds, large hail, and tornadoes across northern New York and New England. In Alberta, Environment Canada issued tornado watches for the Edmonton region, cautioning that storms capable of producing strong gusts and heavy rain were moving in from the foothills. Meanwhile, a separate stationary weather system over Texas is delivering torrential rainfall, with flash flood alerts in effect for Hill Country and the Guadalupe River basin, where some areas could receive up to 15 inches of rain.

Authorities across both countries have urged residents to limit outdoor activity, stay hydrated, and check on vulnerable neighbours. Cooling centres have opened in cities including Toronto and Hamilton. Health officials note that heat-related illnesses — from cramps to heatstroke — increase sharply during such events, though no fatalities from the current wave have been confirmed. The heat is expected to begin easing in the Northeast by the end of the week, but warnings remain in place for much of the affected territory, and the risk of wildfires in California and the West persists amid the dry, scorching conditions.