For their anniversary road trip through the West, an escape from the humid misery of a Louisiana summer, Tyson and Adeline Maddox rented a glimmering convertible.

They have kept the top on. It has been too hot to do anything else.

“Reminds me of the engine room,” Mr. Maddox grumbled of the weather as he left the “Welcome to Fabulous Las Vegas” sign on Wednesday evening, when temperatures were still well into triple digits.

“The heat, it’s just constantly coming,” Ms. Maddox added later. “It’s like being in front of an exhaust pipe.”

So it has been around the Las Vegas area this week. Pedestrians sometimes felt scarcer than jackpots. Playgrounds stood empty and silent. Merely walking through a parking lot meant squinting — not at the sunlight blanketing the region, but at a heat so punishing that eyes hurt without ever actually watering.

At times, the mercury’s ticks upward have come so fast that forecasters, at once awe-struck and unnerved, could hardly keep up.

“Remember 20 minutes ago when hitting 117°F was a big deal?” the local National Weather Service office wrote on social media on Wednesday. “Well, the airport hit 118°F.”