ATIS (Automatic Terminal Information Service) and AWOS (Automated Weather Observation System) serve similar functions to pilots, but ATIS is required to be reviewed by ATC prior to transmission and is often dictated by an air traffic controller on an hourly basis, or when there is a significant change to the weather.
In addition to ATC oversight, ATIS is often supplemented with more detailed weather observations and NOTAMS. ATIS for each airport is updated hourly while the air traffic control tower is in operation. If there is a significant change in the weather or a timely update to the airport operating procedures the ATIS may be updated more than once per hour.
Each ATIS is assignd a NATO phonetic letter beginning with "Alpha," ending with "Zulu." This pattern is repeated unless the broadcast is interrupted for 12 or more hours at which point the next ATIS will be assigned "Alpha".
Some extra information you might find in an ATIS that would not be in an AWOS or ASOS would include: * Instrument or visual approaches in use as well as landing/departing runway(s) * PIREPS: e.g. "At 2016 Z, a Boeing 737 on final to RWY 35 left, reported bases at 1,300" * NOTAMS: e.g. "Warning, Runway 19 has been shortened, 2,500 feet available" * Information on other hazards: e.g. Unauthoried laser illumination event, 1654 Z, green laser reported 4 miles Northwest of runway 5.
These are often available in addition to the ATIS and when the ATIS stops being updated after the tower closes the phone number and radio frequency typically will fall back to broadcasting the AWOS. AWOS is an automated system and its message is updated every minute with information from its weather sensors. The terms AWOS and ASOS are sometimes used interchangeably, but an ASOS (Automated Surface Observing System) is typically a more advanced weather station that generates hourly weather reports and reports on significant weather changes.
ASOS stations provide at least wind and gust information, altimeter setting, temperature and dewpoint as well as sky conditions and cloud ceilings. Many systems are also equipped with a precipitation discriminator which alllows them to tell you if it is raining, snowing, hailing etc and how intensely. Information from these stations is used to generate METARs.
You can read more about ASOS and AWOS here.