Monsoon Dresses New Mexico. My Shot of the Day: July 11, 2012

The monsoon dresses New Mexico by mid-July every year.

Here, the mission church at San Ildefonso Pueblo catches the waning late-morning sunshine of a monsoon afternoon. It didn’t take long for the dark, wet clouds behind the structure to move down the Rio Grande Valley and envelope the village in a wonderful, cool, soaking rain.

May and June are always terribly hot and dry for us in the Southwest.  Then, the heating of the high deserts of the Southwest and northern Mexico cause a shift in the wind patterns that causes a shift in the way moisture flows over the entire continent and moisture is sucked from the Gulf of Mexico up and over our mountains where it builds into the glorious rains that began six days ago.

More from Wikipedia:

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 an easterly to southeasterly wind flow aloft.

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.

San Ildefonso is located west of Espanola, New Mexico.

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