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.”
An official W.M.O. weather station near Santa Rosa recorded a lower temperature that day: 48.6 degrees Celsius, Maximiliano Herrera, a climatologist who maintains a large database of global temperatures, wrote in an email forwarded by Mr. Burt.
Mr. Herrera said he was aware of only two other occasions on which temperatures reached 50 degrees Celsius in April: once last year in Larkana, Pakistan, and once in 1998 in Aquismón, Mexico, although the measurement in Aquismón was also recorded at a regional site. On neither of those occasions did the temperature reach 50.2 degrees, as it did in Nawabshah on Monday.