June is the 2nd driest and one of the three hottest months of the year. The normal rainfall amounts to only 0.13 inches, but as much as 1.70 inches was measured in 1972. There is usually only one day when 0.01 inches or more of rain falls, and the greatest number of such days was only four. This happened only twice, in 1899 and 1932.
The normal mean temperature for the month is 88.2 and has ranged from 93.8 in 1990 down to 79.0 in 1965. In early June, the normal daily high temperature reaches 100 or higher and stays there until the middle of September. Average nighttime temperatures rise from 68 on the 1st to 78 on the 30th. However, on the 27th in 1990, the temperature did not fall any lower than 93. The month averages three days of 110 degrees or higher, but in 1974 there were eighteen such days. The highest temperature ever recorded at Phoenix was 122 degrees on June 26, 1990.
Despite the increasing heat, the air is very dry with the relative humidity even slightly lower than that of May and the lowest of the year. Afternoon readings on the average dip as low as 11 percent. Sunshine is at its maximum and averages 94 percent. June 1916, 1917, 1928, and 1939 all had 100 percent sunshine. The lowest ever recorded was 78 percent in 1931. There are usually only two cloudy days, and the most that has ever been observed was six in 1956.
Toward the end of June, more thunderstorms become visible in the distance along the mountains heralding the arrival of the annual Arizona monsoon, that hot and humid period of midsummer.