The USDOT Volpe Center has for several years monitored the continuous performance of forward scatter-based Runway Visual Range (RVR) visibility monitoring systems at a number of major US airports. This paper examines the dependence of visibility on snowfall as obtained from these measurements and simultaneous weather conditions reported by Automated Surface Observing Systems (ASOS). The airports were originally selected in part to track RVR sensor performance in snow in order to test whether blowing snowfall would compromise sensor performance through interference associated with window contamination of associated optics. In addition, the measurements provide an excellent opportunity to investigate the relationships between visibility at different locations on the airport to snowfall and visibility reports by the ASOS at the same airport. The relationships derived are also useful for examining the interrelationship between snowfall rates and local visibility. The results show that, in general, correlations between RVR visibility measurements and ASOS reports on snowfall are good when the RVR-based data are averaged to conform with the temporal resolution of the ASOS data. However, considerable differences in visibility occur both in time and space over the airport at higher temporal resolutions. That is, many snowfall events exhibit large temporal inhomogeneities with timescales of the order of minutes while ASOS reports are typically hourly. Large spatial inhomogenieties are also often present over the airport domain. The scales of these inhomogeneities are examined by comparing RVR data from arrays of RVR sensors placed along runways throughout the airport.