An automated weather station was installed in May 2001 at treeline on Nevado de Colima, at the western end of the Mexican Neovolcanic Belt (3760 m elevation, 19°34.778' N latitude, 103°37.180' W longitude). Meteorological observations are recorded within the Pinus hartwegii forest from which multi-century tree-ring records were recently developed (Biondi, F., 2001. A 400-year tree-ring chronology from the tropical treeline of North America. Ambio 30: 162-166). We present here the design and operation of the station, as well as a summary of the observations recorded until June 2002. Meteorological patterns are discussed in terms of atmospheric pressure, incoming solar radiation, air and soil temperature, relative humidity, soil moisture, wind speed and direction, and precipitation. Time scales range from hourly to daily to weekly to monthly to seasonal, and shed light on water variability as it relates to high-elevation weather in the North American Monsoon region.