“Heat dome” became mainstream meteorological terminology during the June 2021 Pacific Northwest heat wave, when temperatures reached 116°F in Portland and 121°F in Lytton, British Columbia — shattering records by 10-15°F. The phenomenon killed 1,400+ people across Washington, Oregon, and British Columbia, primarily elderly residents without air conditioning.

Atmospheric Mechanics

A heat dome forms when high-pressure systems trap hot air over regions for extended periods, compressing and heating the atmosphere while blocking cooler air from entering. The term existed in meteorology since the 1990s but exploded into public consciousness when the 2021 Pacific Northwest event contradicted the region’s temperate climate reputation.

The Lytton, BC record of 121°F (49.6°C) occurred June 29, 2021 — the day before a wildfire destroyed 90% of the village. The extreme heat created tinder-dry conditions enabling rapid fire spread that forced complete evacuation within minutes.

Infrastructure Failures & Adaptation

The Pacific Northwest’s limited air conditioning infrastructure (only 44% of Seattle homes had AC in 2021) contributed to the death toll. Power grids strained under unprecedented demand, roads buckled, electrical cables melted, and public transit shut down due to heat-warped tracks.

Subsequent heat domes in 2022 (Texas, Southern Plains) and 2023 (Phoenix’s 31 consecutive days over 110°F) normalized the term while highlighting climate adaptation challenges. Cities began installing cooling centers, expanding tree canopy cover, and updating building codes for passive cooling.

Climate Attribution

Rapid attribution science concluded the 2021 Pacific Northwest heat dome was “virtually impossible” without human-caused climate change — a 1-in-1,000-year event made 150 times more likely by greenhouse gas emissions. The finding accelerated discussions of climate adaptation versus mitigation.

Sources: NOAA, Environment Canada, World Weather Attribution, University of Washington Climate Impacts Group