being present at Yuma 75% of the days studied. Further, the launch of the GOES 9 instrument in 1995 has enabled scientists to detect the amount of water vapor in a column of the atmosphere. By looking at time evolution of precipitable water contours, scientists are able to track the progression of moisture up the gulf and into Arizona. A 1997 modeling study suggests that a mid-latitude westerly disturbance several days prior to a tropical easterly disturbance is necessary for the development of a strong gulf surge. The westerly disturbance increases the amount of subsidence that occurs over the gulf which reduces the depth of the planetary boundary layer. Outflow from deep convection associated with the easterly wave is then confined within the shallow boundary layer. They note that weak surges can occur without the mid-latitude westerly, but that strong surges require both components. In a 2000 Monthly Weather Review article, Fuller and Stensrud show that over the 14 years studied the easterly waves consistently produce gulf surges within three days of the trough passing the tip of Baja California. They stress that the correlation does not allow one to determine causality, but that it is consistent with the conceptual model proposed by Stensrud et al. in 1997. The North American Monsoon Experiment was a field experiment that added many observations to the typical observing system in the Gulf of California such as radiosondes, rain gauges, and radar during the summer of 2004. Several surges took place during this period associated with the passing of a tropical cyclone near the tip of the Baja Peninsula. Many characteristics of surges were seen during these events such as a heat low over the Four Corners region of the United States and increased easterly flow off the Sierra Madre Occidental leading to convective downdrafts. Effects Since one of the major characteristics of a surge is the transport of water, measurements of precipitable water and the dew point can also increase. The increased water vapor increases the amount of convective available potential energy (CAPE), which can result in topographically forced convection. Gulf moisture is typically constrained to central and southern Arizona by the topography of the Mogollon Rim. The moderate steering flow from the surge pushes the convection off the mountains which brings precipitation to the desert valleys. Precipitation from gulf surge events can produce locally heavy rainfall which result in flash floods. In