July Weather

July is the month in which the Arizona monsoon usually arrives from the subtropical latitudes. This monsoon features an inflow of a deep blanket of moisture along with the usual summer high temperatures. A useful definition of a “monsoon day” for the Phoenix area is any day during which the average of the hourly dew point temperatures equals or exceeds 55 degrees F. Over the period of record, the average date of the first day of this event is July 7th.

The monsoon season generally begins in early July and extends through the middle of September; however, it began as early as June 16th in 1925 and as late as July 25th in 1987. The monsoon is not necessarily a permanent feature but may come and go, giving residents brief respites from the muggy weather. On the average there are about 20 monsoon days in July, but there were as many as 31 days in 1984 and as few as seven days in 1987.

Increased thunderstorm activity accompanies the arrival of the monsoon. Thunderstorms are visible on the average during 25 days of the month. On six or seven of these days, the storms are close enough for thunder to be heard at Sky Harbor International Airport. Dust storms associated with these thunderstorms are rather common.

With the increase in thunderstorm activity comes an increase in rainfall. The average for the month is 0.83 inches, but 6.47 inches fell in 1911. The month averages four days with 0.01 inches or more of rain but has had as many as thirteen days in 1896. The probability of a trace or more of rain on any particular day rises from 21 percent on the first of the month to a peak of 54 percent during the last ten days as the monsoon influence intensifies. July is the windiest month of the year with an average velocity of 7.1 m.p.h.

July’s average temperature of 93.5 degrees is the highest of the year, and the month features an average high temperature of 105.9 and an average low of 81.0. The temperature has reached as high as 121 on the 28th in 1995. The lowest ever recorded was 63 on the 4th and 5th in 1912. There are usually 26 days with 100 or higher and five days with 110 or higher during the month. In 1989, there were 16 days with 110 or higher. Nighttime temperatures generally fall to around 80, however, it did not fall below 93 on the 20th in 1989.