When you call flight service or go online for a preflight briefing, most of the current conditions you receive are the product of an Automated Surface Observing System (ASOS) installation at the airport. (Some observations come from Automated Weather Observation Systems; the AWOS is a slightly less sophisticated piece of equipment that performs many of the same functions.) You may have seen an ASOS or an AWOS, taxiing out to depart from your home airport—or while visiting another airport, if yours doesn’t have one.
The ASOS system is a joint effort of the National Weather Service, the FAA, and the Department of Defense. Hourly weather observations are automatically transmitted to NWS and FAA data networks—so are special observations, which are reported automatically when conditions require them. These data reports make up the majority of the METARS you will encounter as you prepare for your flight. They’re also helpful in weather forecasting. Real-time ASOS and AWOS information usually is available in flight, too, accessible over a dedicated radio frequency; many units also have a telephone number you can call if you want to get a weather update on your way to the airport.
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