Even in Pakistan, no stranger to blistering heat, the temperature on Monday stood out: 122.4 degrees Fahrenheit.

The reading came from Nawabshah, a city of 1.1 million people in southern Pakistan, and meteorologists say it is the highest temperature ever reliably recorded, anywhere in the world, in the month of April.

The World Meteorological Organization keeps global temperature records, but not by month, which means Monday in Nawabshah cannot be officially confirmed as the hottest April day. But experts on extreme temperatures say it probably is.

Christopher C. Burt, the author of “Extreme Weather: A Guide and Record Book” and a contributor to Weather Underground, said that 122.4 degrees, or 50.2 degrees Celsius, appeared to be the hottest reliably measured April temperature “in modern records for any location on Earth.” Only one reading might challenge it: 123.8 degrees Fahrenheit, or 51 degrees Celsius, recorded in Santa Rosa, Mexico, in April 2011. But Mr. Burt said that measurement was “questionable because the site was a regional observation site and not of first order.”