In support of the North American Monsoon Experiment 2004 field campaign (NAME 2004), NOAA established and maintained a field site about 100 km north of Mazatlán, Mexico, consisting of wind profilers, precipitation profilers, surface upward/downward looking radiometers, and a 10-m meteorological tower to observe the environment within the North American monsoon. The precipitation profilers enabled the vertical structure of the precipitating cloud systems to be analyzed to better understand the microphysical processes associated with stratiform rain originating from oceanic and continental rain regimes.

In order to provide a climatological context for the profiler observations that were collected for 2 months (July and August 2004), the profiler reflectivity distributions were compared with TRMM Precipitation Radar (PR) reflectivity distributions from the 2004 season over the NAME domain as well as from the 1998-2005 seasons. This analysis places the NAME 2004 observations into context of other monsoon seasons. It also provides a basis for evaluating the representativeness of the structure of the precipitation systems sampled at this location.

In this region of Mexico, the number of rain events observed by the TRMM PR is dependent on geography. The western Mexico portion of the NAME domain was divided into three regions: mountainous land, the coastal plain, and the Gulf of California. The TRMM PR observed more rain events over the mountainous land region than over the coastal plain region. The Gulf of California had the fewest number of observations. When normalized by the total number of observed rain events in each of the three regions, this study found that the frequencies of occurrence of stratiform rain and of stratiform rain with well defined radar brightbands were mostly independent of region. The analysis also revealed that the reflectivity distribution at each height has more year-to-year variability than region-to-region variability. These findings suggest that once a well-defined brightband has developed, the vertical profile of reflectivity relative to the height of the brightband is similar over the mountainous land, the coastal plain, and the gulf regions of western Mexico.