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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.
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