2021 Western North America heat wave

The 2021 Western North America heat wave was an extreme heat wave that affected much of Western North America from late June through early July 2021. The heat wave affected Northern California, Idaho, Western Nevada, Oregon, and Washington in the United States, as well as British Columbia, and in its latter phase, Alberta, Manitoba, the Northwest Territories, Saskatchewan, and Yukon, all in Canada. It also affected inland regions of Central and Southern California, Nevada, and Montana, though the temperature anomalies were not as extreme as in the regions farther north.

The heat wave was characterized as a heat dome because of the extreme temperatures and the exceptionally strong ridge centered over the area, whose probability of formation was linked to the effects of climate change by multiple studies. It resulted in some of the highest temperatures ever recorded in the region, including the highest temperature ever measured in Canada at 49.6 °C (121.3 °F), as well as the highest temperatures in British Columbia, in the Northwest Territories, in the state of Washington as well as a tied record in Oregon. The record-high temperatures associated with the heat wave stretched from Oregon to northern Manitoba, and daily highs were set as far east as Labrador and as far southwest as Southern California.

The extreme heat sparked numerous, extensive wildfires, some reaching hundreds of square kilometers in area. The eponymous Lytton wildfire destroyed the village of Lytton, British Columbia, the day after the site set the record high temperature for Canada. Extreme heat also damaged road and rail infrastructure, forced closures of businesses, disrupted cultural events, and melted snowcaps, in some cases resulting in flooding. The heat wave also caused extensive damage to agriculture across the region, resulting in substantial loss of crop yield and the death of 651,000 farm animals.