In the 1990s, the National Weather Service and the Federal Aviation Administration began deploying the Automated Surface Observing Systems (ASOS). These systems provided the capability to report real-time weather observations, including some types of present weather, as frequently as once every minute. Over 900 of these ASOS stations were installed across the United States, replacing most of the human observers. Despite the benefits offered, many issues were noted, including the inability to discern and report certain precipitation types, particularly drizzle, freezing drizzle, and ice pellets. These and other issues resulted in human observers being retained at roughly 130 ASOS airport locations around the country where high-quality weather observations are essential because of air traffic volume or other factors. The human observers at these locations work in conjunction with the ASOS, manually augmenting the automated weather observations when the ASOS provides erroneous data or when an ASOS observation is missing. To assess the impact of automation on present weather observations, the differences in present weather reports for two decades will be highlighted: 1979–88 (when only human observers reported the present weather observations) and 2005–14 (after the full ASOS network became operational). Comparisons between the decades will be further analyzed to determine the differences at the ASOS locations at which human observers were retained in the later decade, as well as the ASOS locations at which no humans were retained. Both the positive and negative impacts of automation, with an emphasis on aviation impacts, are presented.

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