By Robert Marcos
The summer-like heat in the American West is being caused by a combination of persistent high‑pressure systems, long‑term warming from climate change, and an ever-worsening drought.1
The main condition behind the current weather is the development of strong, stagnant high‑pressure ridges, often called “heat domes,” over the western United States. In these patterns, air sinks over the region, compresses, and warms (adiabatic warming), while clear skies allow intense solar heating of the surface. Because the high pressure suppresses cloud formation and storm systems, the hot air remains parked in place for days or weeks, letting temperatures climb far above normal.2
These weather patterns are occurring on top of a background of human‑driven climate warming, which raises the baseline temperature so that heat waves start from a hotter average and break records more easily. Studies of recent western and Pacific Northwest heat waves show that such extremes would have been virtually impossible, or far less intense, without anthropogenic greenhouse gas emissions. Warmer air also increases “evaporative demand,” meaning the atmosphere pulls more moisture from soils, vegetation, and water bodies, further drying the landscape.3
At the same time, much of the West has been in a long‑running drought or “megadrought,” with declining rain and snowpack, especially in the Southwest and Colorado River basin. Low snowpack and early melt remove a natural cooling reservoir, so land surfaces heat up faster and earlier in the warm season. With drier soils and sparse vegetation, more of the sun’s energy goes directly into raising air temperature rather than evaporating water, amplifying surface heat and extending fire season.4
Finally, ocean–atmosphere patterns over the Pacific, such as persistent ridging and a positive phase of broader circulation patterns, help steer and reinforce these high‑pressure systems over the West in summer. Together, these intertwined conditions—blocking high pressure, climate‑driven warming, deepening drought, and altered atmospheric circulation—have produced the unusually intense and frequent summertime heat now characterizing the American West.5
