A factor that influences transit ridership but has not received much attention from researchers is weather. This paper examines the effects of weather on bus ridership in Pierce County, Washington, for the years 2006–2008. Separate ordinary least squares regression models were estimated for each season, as weather conditions may have different effects depending on the time of year. Four weather variables were considered: wind, temperature, rain, and snow. High winds negatively affected ridership in winter, spring, and autumn. Cold temperatures led to decreases in ridership in winter. Rain negatively affected ridership in all four seasons, and snow was associated with lower ridership in autumn and winter. These results suggest that adverse weather conditions can have a negative effect on transit ridership.