The relentless heat is also reinforcing drought that continues to reshape landscapes and severely burden water resources, while simultaneously setting the stage for a potentially disastrous wildfire season.
The big picture
On Thursday, the heat was already beginning to gather, but the worst was expected Friday into Monday. At least 28 million people are slated to experience highs in the triple digits over the upcoming week.
The exceptional temperatures are thanks to a “heat dome,” or a ridge of high pressure, becoming established over the Four Corners region. It will meander west in the coming days, reinforced by a secondary zone of high pressure cresting to the north in southwest Canada on Friday. By Saturday, that additional high pressure will swing through Alberta and Saskatchewan; the synergy between the two will yield a multiday stretch of highs 20 degrees or more above average.
Excessive heat warnings blanket most of California, Nevada, western Arizona and western Utah, while watches cover interior parts of Oregon and southern Idaho.