and direction at several altitudes in the atmosphere in what is known as a vertical wind profile. The first indication of a gulf surge is a change in the surface wind direction at Yuma, Arizona, with the winds switching from westerly to south-easterly. This flow tends to get wider and deeper as the surge progresses. During the monsoon, there is a pressure difference between the heat low that is present over the Southwestern United States and the relative high pressure over the northern portion of the gulf. Winds will blow from the south due to the pressure gradient force. Typically, during a traditional surge, a large mesoscale convective system is located off the southern tip of the Baja peninsula. Flow around such a low pressure system is cyclonic, which corresponds to counter-clockwise. Some of this circulation will make its way into the gulf and get funneled northward towards the southwestern United States like a waveguide. As this moist air travels northward, it encounters the already present southerly winds and gets pushed into southern Arizona. The high pressure area over the northern gulf tends to push the moisture surge to the east towards the Tucson area. Gulf of California moisture surges were first scientifically documented in the early 1970s. John Hales, formerly of the Phoenix National Weather Service office, wrote in the April 1972 edition of Monthly Weather Review that gulf surges are related to large areas of cloud masses that are transported northward up the Gulf of California and spill into southern Arizona. He wrote that a surge resembles a large sea breeze. Ira Brenner continued studying gulf surges in 1974, and like Hales found that they resemble a large sea breeze with warm, moist air transported northward in the lowest of the atmosphere. Brenner was the first to suggest that easterly waves may be important in the initiation of a gulf surge. The mid-1990s saw a resurgence of interest in the North American Monsoonal system. Using data collected during the SWAMP–90 field campaign, Michael Douglas found that the surge of moisture was associated with a low level jet. The jet was strongest from to above the surface. It also showed diurnal variations, with air traveling downslope toward the Gulf of California in the mornings and upslope in the evenings. During the field campaign, the jet was found to be a consistent feature during widely varying synoptic conditions; with it