Evening Light, After the Monsoon Rains
The Arizona monsoon is a pronounced increase in thunderstorms and rainfall over large areas of the southwestern United States and northwestern Mexico, typically occurring between June and mid-September.
During the monsoon, thunderstorms are fueled by daytime heating and build up during the late afternoon-early evening. These storms usually dissipate by late night, and the next day starts out fair, with the cycle repeating daily. The monsoon loses its energy by mid-September when drier and cooler conditions are reestablished over the region.
Geographically, the North American monsoon precipitation region is centered over the Sierra Madre Occidental in the Mexican states of Sinaloa, Durango, Sonora and Chihuahua. The North American Monsoon is not as strong or persistent as its Indian counterpart, mainly because the Mexican Plateau is not as high or as large as the Tibetan Plateau in Asia.
However, the North American Monsoon shares most of the basic characteristics of its Indian counterpart. There is a shift in wind patterns in summer which occurs as Mexico and the southwest U.S. warm under intense solar heating. As this happens, the flow reverses. The prevailing winds start to flow from moist ocean areas into dry land areas.
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 late June or early July. It extends into the southwest United States as it matures in mid-July.
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.
Brief but often torrential thunderstorms can occur, especially over mountainous terrain. This activity is occasionally enhanced by the passage of tropical waves and the entrainment of the remnants of tropical cyclones.
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.
Flash flooding is a serious danger during the monsoon. Dry washes can become raging rivers in an instant, even when no storms are visible as a storm can cause a flash flood tens of miles away; it is therefore wise to avoid camping in a dry wash during the monsoon. Lightning strikes are also a significant danger. Because it is dangerous to be caught in the open when these storms suddenly appear, many golf courses in Arizona have thunderstorm warning systems.
Evening Light, After the Monsoon Rains
The Arizona monsoon is a pronounced increase in thunderstorms and rainfall over large areas of the southwestern United States and northwestern Mexico, typically occurring between June and mid-September.
During the monsoon, thunderstorms are fueled by daytime heating and build up during the late afternoon-early evening. These storms usually dissipate by late night, and the next day starts out fair, with the cycle repeating daily. The monsoon loses its energy by mid-September when drier and cooler conditions are reestablished over the region.
Geographically, the North American monsoon precipitation region is centered over the Sierra Madre Occidental in the Mexican states of Sinaloa, Durango, Sonora and Chihuahua. The North American Monsoon is not as strong or persistent as its Indian counterpart, mainly because the Mexican Plateau is not as high or as large as the Tibetan Plateau in Asia.
However, the North American Monsoon shares most of the basic characteristics of its Indian counterpart. There is a shift in wind patterns in summer which occurs as Mexico and the southwest U.S. warm under intense solar heating. As this happens, the flow reverses. The prevailing winds start to flow from moist ocean areas into dry land areas.
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 late June or early July. It extends into the southwest United States as it matures in mid-July.
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.
Brief but often torrential thunderstorms can occur, especially over mountainous terrain. This activity is occasionally enhanced by the passage of tropical waves and the entrainment of the remnants of tropical cyclones.
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.
Flash flooding is a serious danger during the monsoon. Dry washes can become raging rivers in an instant, even when no storms are visible as a storm can cause a flash flood tens of miles away; it is therefore wise to avoid camping in a dry wash during the monsoon. Lightning strikes are also a significant danger. Because it is dangerous to be caught in the open when these storms suddenly appear, many golf courses in Arizona have thunderstorm warning systems.