Weather conditions are a key factor in deciding where to build telescope facilities. It is also a critical factor when planning and designing large surveys. Siding Spring Observatory, located in Northern New South Wales, Australia, has been a national hub for optical astronomy for decades. Weather data have been gathered from multiple sources on site and analyzed to show long term trends in wind, humidity, temperatures, and observing conditions on site. A gradual decrease in humidity was observed due to the recent drought, a trend that is expected to continue into the future. Downtime due to high humidity occurs most in winter, with 17.5% of observing time sitting at >90%. Wind direction and speeds are highly variable across the mountain. Predominant winds are NNW in summer (December–February), and S in winter (June–August). Strong gusts in excess of 55 ms−1 can rarely be experienced near the apex of the mountain, however, the majority of the mountain does not experience this, and the median wind speed is 3.4 ms−1. Temperatures are consistent across the mountain, with a median of 14.1°C. Diurnal temperature variations are largest in summer, at 11°C. 46% of nights are cloudy, with a further 9%–29% having poor viewing conditions depending on wavelength range.