But more fundamentally a 'Monsoon' is linked more to a wind shift rather than precipitation. Again, for India, during the winter dry period, the airflow comes from high pressure to the north the dry Himalayas and Siberia. For the summer, the desert of western India heats up and low pressure forms. During the winter time, the primary wind flow in Arizona is from the west or northwest from California and Nevada. As we move into the summer, the winds shift to a southerly or southeasterly direction.
Moisture streams northward from the Pacific Ocean and the Gulf of Mexico.
This shift produces a radical change in moisture conditions statewide. Such a change, together with daytime heating, is the key to the Arizona monsoon. These two features combine to create strong southerly flow over Arizona. The southerly winds push moisture north-ward from Mexico. The exact source region for the moisture of the Arizona monsoon is unknown.