The first week of summer is getting off to an especially hot start in the American Southwest. According to ABC News, temperatures reached 118°F on Monday, June 19, tying the regional record for that day set last year. Today, Tuesday, June 20, the mercury is expected to climb even higher, and airlines in Phoenix are canceling flights as a precaution.

American Airlines grounded close to 50 flights scheduled to take off from Sky Harbor International Airport in Phoenix Tuesday morning, The Arizona Republic reports. With the National Weather Service predicting highs of 119°F, the Bombardier CRJ aircraft used by the airline for regional flights has been deemed unfit to travel.

The maximum operating temperature of the Bombardier CRJ aircraft is 118°F—at that point, experts worry that the air is no longer dense enough for the plane to take off and fly efficiently. Extreme heat isn’t a common problem for airlines, with temperatures approaching the 120s in the Southwest less than one day a year on average. But this summer is already shaping up to be one for the record books. Above-average heat is projected to scorch the region from now through September. The forecast fits into a recent trend of intense Southwestern summers which scientists believe are connected to climate change.

While many local flyers will be inconvenienced by the heat today, travelers flying beyond Arizona can expect a smooth trip. Larger jets, like Boeing and Airbus, have maximum operating temperatures of 126°F and 127°F, respectively—higher than any temperature that's been recorded in Phoenix to date.

[h/t ABC News]