Climate
Tucson has two major seasons, summer and winter; plus three minor seasons: fall, spring, and the monsoon.
Summer is characterized by low humidity, clear skies, and daytime high temperatures that exceed 100 degrees Fahrenheit. The average overnight temperature ranges between 68 °F and 85 °F.
The monsoon season can begin any time from mid-June to late July, with an average start date around July 3. It typically continues through August and sometimes into September. During the monsoon, the humidity is much higher than the rest of the year. It begins with clouds building up from the south in the early afternoon followed by intense thunderstorms and rainfall, which can cause flash floods. Large areas of the city do not have storm sewers, so monsoon rains flood the main thoroughfares, usually for no longer than a few hours. A few underpasses in Tucson have "feet of water" scales painted on their supports to indicate whether they can be safely forded by an automobile during a rainstorm. The evening sky at this time of year is often pierced with dramatic lightning strikes.
Fall lasts from late October to November or December. It is much like summer, and similarly dry, with days above 100 degrees typical into early October. Average daytime highs of 84 °F, with overnight lows of 55 °F, constitute typical fall weather.
Winters in Tucson are mild relative to other parts of the United States. Daytime highs in the winter range between 64 °F and 75 °F, with overnight lows between 30 °F and 44 °F. Although rare, snow has been known to fall in Tucson, usually a light dusting that melts within a day.
Spring begins in late February or March, and is characterized by rising temperatures and several weeks of vivid wildflower blooms. Daytime average highs range from 72 °F in March to 88 °F in May with average overnight lows in March of 45 °F and in May of 59 °F.
(Source: Wikipedia.org)
