Phoenix, the capital of Arizona, sits in the Salt River Valley of the Sonoran Desert in the southwestern United States, on a low, flat basin ringed by mountains at approximately 33.45°N, 112.07°W. It has a hot desert climate (Köppen BWh) — one of the hottest major cities in the United States — with extremely hot summers, mild winters, abundant sunshine and very little rain.

Summer, from May to September, is long and blisteringly hot, with July the hottest month — average highs around 41°C and frequent spells above 45°C, with the temperature having reached 50°C. The dry heat is punishing, and the sprawling city's concrete and asphalt create a strong urban heat island that keeps nights sweltering. From about July to September the North American monsoon brings bursts of humidity, dramatic dust storms (haboobs) and sudden, sometimes flooding thunderstorms.

Winter, from December to February, is warm, sunny and pleasant, with January the coolest month — average highs around 19–20°C and mild nights near 7–8°C. Frost is rare in the city. This mild, dry, sun-drenched season is comfortably the best time of year and draws many winter visitors escaping colder climates, with clear blue skies the near-constant norm.

Phoenix is extremely dry, receiving only around 180–200 mm of rain a year, falling in two seasons — gentle winter rains from Pacific storms and the summer monsoon thunderstorms of July to September — with June the driest month. Even so, rain is scarce and sunshine is near-relentless, with the city averaging over 3,800 hours a year. Live rainfall, humidity, and pressure readings for the city are shown in the panels above.

The North American monsoon is the most dramatic feature of Phoenix's weather: from July to September, moisture surging up from the tropics sets off violent thunderstorms, flash floods and towering walls of dust called haboobs that can engulf the city. The rest of the year is defined by relentless sun and extreme summer heat, intensified by the urban heat island, which has made rising temperatures a growing public-health concern.

To follow any single measurement in Phoenix more closely, use our live instruments: the online barometer for atmospheric pressure, the thermometer for temperature, the hygrometer for humidity, the anemometer for wind speed, the wind vane for wind direction, and the rain gauge for rainfall.