The Low-Down on the West's Heat Wave: What's Causing It and Why Hot Nights Are So Dangerous

Excessive heat is the No. 1 weather killer in the United States and it's at its most dangerous when it doesn't cool down at night.
The current heat wave over California, Nevada, Arizona and New Mexico has temperatures hitting triple digits, with little relief at night. Hot weather is also baking the rest of the far West, including Washington, Oregon, Idaho, and parts of Utah and Montana.
Pennsylvania State University climate scientist Michael Mann said there's an element of randomness in the current weather. Yet with all-time heat records in the past few years being broken at three times the expected rate, he said, "there can be little doubt that climate change and global warming are playing a role."

The Low-Down on the West's Heat Wave: What's Causing It and Why Hot Nights Are So Dangerous