This data set, updated annually from the National Climatic Data Center (NCDC), contains summary of the day first order station surface weather observations. The stations are operated by the National Weather Service (NWS), the Federal Aviation Administration (FAA), the U.S. Air Force (Air Weather Service), and the U.S. Navy (Navy Weather Detachment). The NWS and FAA sites are located in the contiguous U.S., Alaska, Puerto Rico, Hawaii and other Pacific Islands. The Air Force and Navy operate stations worldwide.

The observations are generally recorded midnight to midnight for the 24-hour period. The major data parameters are wind, maximum temperature, minimum temperature, wet-bulb temperature, dew-point temperature, maximum relative humidity, minimum relative humidity, precipitation, station pressure, sea level pressure, snowfall, snow depth, and present weather.

The earliest data is for 1881 but most stations begin in 1948. There are currently about 630 first order stations reporting. Periods of record vary widely among the stations.