This worldwide collection of surface weather observations is
produced at the National Climatic Data Center (NCDC) from NCDC
Surface Airway Hourly Observations (TD3280
[http://rda.ucar.edu/datasets/ds470.0/]), U.S.A.F. DATSAV3 Surface
Hourly Observations (TD9956
[http://rda.ucar.edu/datasets/ds463.2/]), and NCDC Cooperative
Hourly Precipitation (TD3240
[http://rda.ucar.edu/datasets/ds505.0/]). Observations are all in
the same ASCII format.
Mandatory data includes pressure, temperature, dew-point,
visibility, sky condition, and wind observation, but there may also
be additional data, data remarks, or data element quality sections.
The earliest data is for 1901. The earliest years have the least
volume of data, a few hundred megabytes; the volume in the
1950s-early 1960s increased by a factor of 10-20; 1965-1972 shows a
decrease because of a loss of data; beginning in 1973 with about 5
gigabytes of data, volume has gradually increased to about 20
gigabytes per year. There are now about 10,000 active stations.