A first-order weather station is a site at which weather observations were taken by National Weather Service employees or other certified observers. Observations were usually taken hourly or as needed around the clock. Daily summary statistics are also recorded. A comprehensive array of weather variables were recorded, such as barometric pressure, air and dew point temperatures, wind speed and direction, relative humidity, precipitation type and amount, and cloud cover and visibility. Many first-order weather stations were located at major airports.