This global summary of the day and month data set is obtained on a delayed monthly basis from the Climate Prediction Center (CPC) of the National Centers for Environmental Prediction (NCEP). CPC extracts surface synoptic weather observations from the Global Telecommunications System (GTS) and performs limited automated validation of the parameters. The data is then summarized for all reporting stations on a daily basis to current operational requirements related to the assessment of crop and energy production.

Data coverage begins in 1979. In 1987 there is a format change and additional parameters were added. Major parameters include maximum temperature, minimum temperature, precipitation, vapor pressure, sea level pressure, maximum relative humidity, and minimum relative humidity. If the maximum or minimum temperatures are not reported, they are estimated from reported air temperatures in the regular synoptic reports when sufficient data exist. Starting in 1994, total sky cover, 3-hourly wind direction and speed, and total snow depth are included. There are approximately 8900 actively reporting stations. Periods of record vary widely among the stations.

CAUTIONARY NOTE: NCEP incorrectly decoded the wind units indicator from February 1, 2001 until 1500 UTC on June 11, 2002, which caused a knots versus meters-per-second problem. Not all stations were affected. Users may, with caution, apply the knots or meters-per-second conversion where it appears to be the correct choice.