In order to fill in the observation gap prior to the time when commercial aviation began in the U.S., The NCDC Climate Data Modernization Program (CDMP) retrieved surface observations taken two to four times daily beginning as early as 1893 at the City Weather Bureau Offices. Through 1936 observations were taken twice daily; then in 1937 the general practice was to record four observations per day. Since this data overlaps with the pre-1948 hourly dataset DSI-3851 (surface airways observations) (C00623), data for each station were not keyed once their observations overlapped with the DSI-3851 data which generally contains more observations per day. The data elements are as follows: station pressure, sea level pressure, dry and wet bulb temperature, dew point, maximum and minimum temperature, wind direction and speed, precipitation, cloud amount and type, ceiling, state of weather and visibility. It should be noted that not all elements are present for all stations in this dataset, and that ceiling and visibility observations did not begin at the city offices until the 1930's. Official surface weather observation standards can be found in the Circular N manuals.

When hourly observations were not conducted, observational data from stations were keyed. These data can be found in DSI-3850 (C00622). The complimentary pre-1948 hourly observations dataset is DSI-3851 (surface airways observations) (C00623).