Phoenix has a subtropical arid climate, with extremely hot summers and warm winters. The average summer high temperature is among the hottest of any populated area in the United States and approaches those of cities such as Riyadh and Baghdad. The temperature reaches or exceeds 100°F (38°C) on an average of 110 days during the year, including most days from late May through early September, and highs top 110 °F (43 °C) an average of 18 days during the year. On June 26, 1990, the temperature reached an all-time recorded high of 122 °F (50 °C).
Overnight lows greater than 80 °F (27 °C) occur frequently each summer, with the average July low being 81 °F (27 °C) and the average August low being 80 °F (27 °C). On average, 67 days throughout the year will see the nighttime low at or above 80 °F (27 °C). The all time highest low temperature ever recorded in Phoenix was 96 °F (36 °C), which occurred on July 15, 2003.
Precipitation is sparse during a large part of the summer, but the influx of monsoonal moisture, which generally begins in early July and lasts until mid-September, raises humidity levels and can cause heavy localized precipitation and flooding occasionally. Winter months are warm, with daily high temperatures ranging from the mid-60's to low 70's (18-22°C), and low temperatures rarely dipping below 40 °F (4 °C).

Phoenix from North Mt Preserve
Phoenix averages 85% of possible sunshine and receives scant rainfall, the average annual total at Phoenix Sky Harbor International Airport being 8.3 inches (210 mm). March is the wettest month of the year (1.07 inches or 27 mm) with June being the driest (0.09 inches or 2 mm). Although thunderstorms are possible at any time of the year, they are most common during the monsoon from July to mid-September as humid air surges in from the Gulf of California. These can bring strong winds, large hail, or rarely, tornadoes. Winter storms moving inland from the Pacific Ocean occasionally produce significant rains but occur infrequently. Fog is rare but can be observed from time to time during the winter months.
On average, Phoenix has only 5 days per year where the temperature drops to or below freezing. The long-term mean date of the first frost is December 15 and the last is February 1; however, these dates do not represent the city as a whole because the frequency of freezes increases the further one moves outward from the urban heat island. Frequently, outlying areas of Phoenix see frost, but the airport does not. The earliest frost on record occurred on November 3, 1946, and the latest occurred on April 4, 1945. The all-time lowest recorded temperature in Phoenix was 16 °F (-9 °C) on January 7, 1913.
Snow is extremely rare in the area but is possible. Snowfall was first officially recorded in 1896, and since then, accumulations of 0.1 inches (0.25 cm) or greater have occurred only seven times. The heaviest snowstorm on record dates to January 20, 1937 - January 21, 1937, when 1 to 4 inches (2.5 to 10 cm) fell in parts of the city and did not melt entirely for four days. Before that, 1 inch (2.5 cm) had fallen on January 20, 1933. On February 2, 1939, 0.5 inches (1.3 cm) fell. Most recently, 0.4 inches (1.0 cm) fell on December 21, 1990 - December 22, 1990. Snow also fell on March 12, 1917, November 28, 1919, December 11, 1985 and just after Christmas 2008.