For all you dunces like me that hasn't a clue what any of this code means, I looked it up and added my own comments to the example.

Example:
URNT11 KNHC 161227
AF967 0212A LILI OB 08 KNHC
97779 code
12314 time gmt
40169 lat
82508 long
04000 altitude
22020 wind dir / wind speed
25218
/0007 pressure 1007mb
42115;

The first two lines are the heading of the message.

The first group is almost always "97779".

Time. The first four numbers in the second group is the time of the observation, in Greenwich Mean Time (subtract 4 hours to get Eastern Daylight Time, 5 hours to get Central Daylight Time, or subtract 6 hours to get Central Standard Time). In the example, "1231" is 1231 GMT, or 7:31 a.m. CDT.

Location. Find the latitude in the last three digits of the third group, and the longitude in the first three digits of the second group. The latitude and longitude are reported in degrees and tenths. If the longitude is 100.0 degrees or above, the first "1" is dropped in the code, for example, 104.3W is coded "043"; you need to look elsewhere in the code if you aren't sure if that was 4.3W or 104.3W. In the above example, the aircraft was at 16.9N 82.5W.

Altitude. The first three digits of the fifth group tells you approximately how high the aircraft is flying. It is coded in "decameters", which means you need to multiply this number by 10 to convert to meters, then multiply by 3.281 if you want to convert to feet. In the above example, the altitude is coded "040" = 40 dm = 400 m = 1312 ft. This tells you the aircraft is on a low-level mission.

Winds. The sixth group is the wind measured at the altitude of the airplane. The first two digits are the wind direction, to the nearest ten degrees. Wind direction is reported similar to compass headings, where 360 or 0 degrees is north. In the code, 09=east, 18=south, and 27=west. The next three digits is the wind speed in knots. Multiply by 1.152 to convert to miles per hour. In the above example, "22020" is a wind of 220 degrees (blowing out of the southwest) at 020 knots (23 mph).

Pressure. The eighth group, always begins with a "/". The second digit tells you at what level the aircraft is flying. A "0", as above, shows the aircraft is flying below 1500 feet and is estimating sea-level pressure. The next three digits is the pressure or height data. Only if the second digit is a "0" will this be sea-level pressure (in millibars). In the above example, the sea-level pressure is 1007 millibars. This is a complicated group, and for aircraft flying above 1500 feet, see the full decode below.