Wikipedia, "During the monsoon, thunderstorms are fueled by daytime heating and build up during the late afternoon–early evening. Typically, these storms dissipate by late night, and the next day starts out fair, with the cycle repeating daily." This must be a blessed relief from the otherwise high temperatures of summertime in this region.
Rather than try to summarize the causes and effects, I'll just copy from Wikipedia wholesale, because I find this most interesting. (Yes, I did supply the link above, but it's easier if it's right here, right?)
The North American monsoon is associated with an area of high pressure called the subtropical ridge that moves northward during the summer months and a thermal low (a trough of low pressure which develops from intense surface heating) over the Mexican Plateau and the Desert Southwest of the United States. The monsoon begins in late May to early June in southern Mexico and quickly spreads along the western slopes of the Sierra Madre Occidental, reaching Arizona and New Mexico in early July. The monsoon extends into the southwest United States as it matures in mid-July, when an area of high pressure, called the monsoon or subtropical ridge, develops in the upper atmosphere over the Four Corners region, creating wind flow aloft from the East or South-East.It seems this year the monsoon is centered a bit more westerly than usual, which creates a greater effect out here on the margin of the continent (though it's more complicated than that, of course).
Pulses of low level moisture are transported primarily from the Gulf of California and eastern Pacific. The Gulf of California, a narrow body of water surrounded by mountains, is particularly important for low-level moisture transport into Arizona and Sonora. Upper level moisture is also transported into the region, mainly from the Gulf of Mexico by easterly winds aloft. Once the forests of the Sierra Madre Occidental green up from the initial monsoon rains, evaporation and plant transpiration can add additional moisture to the atmosphere which will then flow into Arizona. Finally, if the southern Plains of the U.S. are unusually wet and green during the early summer months, that area can also serve as a moisture source.
Monsoons play a vital role in managing wildfire threat by providing moisture at higher elevations and feeding desert streams. Heavy monsoon rain can lead to excess winter plant growth, in turn a summer wildfire risk. A lack of monsoon rain can hamper summer seeding, reducing excess winter plant growth but worsening drought.
Craig Childs's The Desert Cries: A Season of Flash Floods in a Dry Land. That was the monsoon calling. It is beautiful and refreshing, as well as destructive and deadly. "I sometimes think that, in the perfect Eden, there are no floods," writes Childs. "In Utopia, a person never dies fighting beneath muddy waves. Then I am glad to not live in such barren places as these. Floods belong to a fertile and dynamic land. We cannot control elements of danger, magnificence, and prowess in the world. To wish them away or to tear them into survivable pieces is to wish for a less genuine Earth."
P.S. I had no clue what to write about today, so I resorted to a website of 365 writing prompts. The first one was "1. Outside the Window: What’s the weather outside your window doing right now? If that’s not inspiring, what’s the weather like somewhere you wish you could be?" I might be using that website more often: it's useful!