First three lines of each file is a header with meta data information from ISH documentation.

YEAR USAF   WBAN  STATION NAME                  CTRY  ST CALL  LAT    LON     E
LEV(.1M)

FORMAT: 
%12s %5s %1s %5s %1s %5s %1s %5s %1s, yyyymmddhh, temperature, temperature qc, dew point temperature, dew point temperature qc, sea level pressure, sea level pressure qc, station level pressure, station level pressure qc


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Below are the descriptions of each variable from ISH documentation.

ATMOSPHERIC-PRESSURE-OBSERVATION sea level pressure
The air pressure relative to Mean Sea Level (MSL).
MIN: 08600 MAX: 10900 UNITS: Hectopascals
SCALING FACTOR: 10
DOM: A general domain comprised of the numeric characters (0-9).
99999 = Missing.

ATMOSPHERIC-PRESSURE-OBSERVATION sea level pressure quality code
The code that denotes a quality status of the sea level pressure of an
ATMOSPHERIC-PRESSURE-OBSERVATION.
DOM: A specific domain comprised of the characters in the ASCII character set.
0 = Passed gross limits check
1 = Passed all quality control checks
2 = Suspect
3 = Erroneous
4 = Passed gross limits check , from DSI-3280 or NCDC ASOS/AWOS
5 = Passed all quality control checks, from DSI-3280 or NCDC ASOS/AWOS
6 = Suspect, from DSI-3280 or NCDC ASOS/AWOS
7 = Erroneous, from DSI-3280 or NCDC ASOS/AWOS
9 = Passed gross limits check if element is present

AIR-TEMPERATURE-OBSERVATION dew point temperature
The temperature to which a given parcel of air must be cooled at constant pressure and water vapor
content in order for saturation to occur.
MIN: -0982 MAX: +0368 UNITS: Degrees Celsius
SCALING FACTOR: 10
DOM: A general domain comprised of the numeric characters (0-9), a plus
sign (+), and a minus sign (-).
+9999 = Missing.
AIR-TEMPERATURE-OBSERVATION dew point quality code
The code that denotes a quality status of the reported dew point temperature.
DOM: A specific domain comprised of the characters in the ASCII character set.
0 = Passed gross limits check
1 = Passed all quality control checks
2 = Suspect
3 = Erroneous
4 = Passed gross limits check , from DSI-3280 or NCDC ASOS/AWOS
5 = Passed all quality control checks, from DSI-3280 or NCDC ASOS/AWOS
6 = Suspect, from DSI-3280 or NCDC ASOS/AWOS
7 = Erroneous, from DSI-3280 or NCDC ASOS/AWOS
9 = Passed gross limits check if element is present

ATMOSPHERIC-PRESSURE-OBSERVATION station pressure rate
The atmospheric pressure at the observation point.
MIN: 04500 MAX: 10900 UNITS: Hectopascals
SCALING FACTOR: 10
DOM: A general domain comprised of the numeric characters (0-9).
99999 = Missing.

ATMOSPHERIC-PRESSURE-OBSERVATION station pressure quality code
The code that denotes a quality status of the station pressure of an
ATMOSPHERIC-PRESSURE-OBSERVATION.
DOM: A specific domain comprised of the characters in the ASCII character set.
0 = Passed gross limits check
1 = Passed all quality control checks
2 = Suspect
3 = Erroneous
4 = Passed gross limits check , from DSI-3280 or NCDC ASOS/AWOS
5 = Passed all quality control checks, from DSI-3280 or NCDC ASOS/AWOS
6 = Suspect, from DSI-3280 or NCDC ASOS/AWOS
7 = Erroneous, from DSI-3280 or NCDC ASOS/AWOS
9 = Passed gross limits check if element is present

FORMAT: 
%12s %5s %1s %5s %1s %5s %1s %5s %1s, yyyymmddhh, temperature, temperature qc, dew point temperature, dew point temperature qc, sea level pressure, sea level pressure qc, station level pressure, station level pressure qc

Reference

FEDERAL CLIMATE COMPLEX DATA DOCUMENTATION FOR INTEGRATED SURFACE DATA, March 2, 2007, National Climatic Data Center
National Climatic Data Center
Air Force Combat Climatology Center
Fleet Numerical Meteorology and Oceanography Detachment
151 Patton Avenue
Asheville, NC 28801-5001 USA