Yuma is noted for its weather extremes. Of any populated place in the contiguous United States, Yuma is the driest, the sunniest, and the least humid, has the lowest frequency of precipitation, and has the highest number of days per year—175—with a daily maximum temperature of 90 °F , with extremely hot summers and warm winters. Atmospheric humidity is usually very low, except during what are called “Gulf surges”, when a maritime tropical air mass from the Gulf of California is drawn northward, usually in connection with the summer monsoon or the passage of a tropical storm to the south.
The sun is said to shine during about 90% of the daylight hours, making Yuma one of the sunniest places in the world. The city receives the most recorded mean sunshine of anywhere on Earth, although the equipment used by the United States tends to provide higher sunshine estimates than the traditional Campbell–Stokes recorder.
On average, Yuma receives 3.36 inches (85 mm) of rain annually. Even in the wettest year of 2005, only 7.39 in (188 mm) fell. The driest year at Yuma Airport was 2007, with only 0.15 in (3.8 mm) recorded. On average, the wettest months of the year are during the monsoon months of August and September, and December, when moisture from winter storms arrives from the Pacific Ocean. June is the driest month, with drought virtually absolute.
In 1995, Yuma recorded its all-time high temperature of 124 °F (51 °C). The lowest recorded temperature was in the Yuma-Mesa area in January 2007. The temperature fell to 21 °F (−6 °C) for approximately two hours, harming many crops grown in and around Yuma. Citrus suffered the most, particularly the lemon crop. According to an Arizona Department of Agriculture report in February 2007, there was a 75% to 95% loss of crop and trees. On average, the temperature reaches freezing point in less than one year in four, and there are 118 days per year during which the temperature reaches or exceeds 100 °F (38 °C), usually from April through October. During July and August the temperature fails to reach 100 °F (38 °C) on only a few days.
In 1997, the desert city sustained a full tropical storm after Hurricane Nora made landfall at the mouth of the Colorado River and quickly moved due north along it. This rare event cut power to 12,000 customers in Yuma, and dropped 3.59 inches (91 mm) of rain at Marine Corps Air Station Yuma. The last time a hurricane had hit near Yuma was in mid-August 1977, when similar rainfalls were recorded.