The U.S. National Weather Service issued a formal warning Friday that a widespread, intensely powerful heat wave will descend on drought-stricken western states over the coming weekend, bringing dangerously high temperatures that could break long-standing all-time heat records across the region.
A expanding heat dome – a stationary high-pressure system that traps hot air close to the ground – will spread southward and eastward from the Pacific Northwest across the northern Great Plains, with forecast models projecting peak temperatures could reach 110 degrees Fahrenheit (43 degrees Celsius) in multiple areas by Sunday.
The NWS warned that the combination of blistering daytime high temperatures and unusually warm overnight lows that offer little chance for relief will drive rapidly increasing heat stress across the region, pushing the agency’s HeatRisk index to widespread major levels and extreme levels in local hotspots. The “extreme” classification is the highest category on the NWS’ risk scale, meaning dangerous heat conditions that can threaten the health of any individual without access to consistent cooling and adequate hydration. Regional power grids are also bracing for heavy strain as residents run air conditioning continuously to beat the heat.
Climate scientists say this extreme heat event is far from a random weather event, shaped heavily by decades of human-caused climate change. Marc Alessi, a science fellow at the Union of Concerned Scientists, told Agence France-Presse that today’s heat events are unfolding in a fundamentally altered global climate system. “Right now, every ocean basin on the planet is experiencing marine heat waves, which are releasing massive amounts of extra heat into the atmosphere,” Alessi explained. “This is reshaping global weather patterns and creating conditions that produce these completely unprecedented heat events.”
Alessi added that a developing strong El Niño event in the equatorial Pacific is also contributing to the formation of the western U.S. heat dome. “We are already seeing dramatic warming of sea surface temperatures in the central Pacific,” he noted. This warm water alters how storm energy moves from the tropics to the mid-latitudes, which in turn shifts the jet stream in a pattern that allows the heat dome to strengthen and stall over the western United States.
This weekend’s heat wave comes on the heels of similar extreme events that baked the central and eastern U.S. just last week, following major heatwaves that swept across Europe earlier this summer. A recent analysis from the international research group World Weather Attribution confirmed that the previous deadly hot spell that hit the U.S. during its 250th Independence Day celebrations would have been virtually impossible to occur without the influence of human greenhouse gas emissions driving climate change.
Beyond the direct health risks of extreme heat, the hot, dry conditions are also set to dramatically increase wildfire risk across the already parched West. Most of the western U.S. is already facing conditions ranging from abnormal dryness to severe multi-year drought, and hot, gusty winds will create ideal conditions for fast-spreading wildfires. Heat domes also spawn dry thunderstorms, where rain evaporates completely before reaching the ground, leaving lightning strikes that can easily ignite new blazes across dry vegetation. A risk assessment from the U.S. National Interagency Fire Center identifies Washington, Oregon, Idaho, Montana, and Wyoming as facing particularly elevated wildfire danger this weekend.