ASOS is the primary network of automated weather stations in the United States, typically located at airports. These stations report hourly (and special) meteorological observations, including temperature, wind speed/direction, precipitation, sky cover, and visibility, serving as the official “ground truth” for aviation and forecasting.
Unlike hobbyist weather stations, ASOS units are strictly maintained by the FAA and the National Weather Service, ensuring high-quality, standardized sensors. When a company claims a “1-degree accuracy” in their forecast, they are almost always benchmarking against ASOS data. Professionals search for “ASOS sensor maintenance logs” if they suspect a specific station is “drifting” (e.g., reporting temperatures that are consistently too high due to asphalt proximity).
ASOS uses a laser ceilometer that looks straight up; it cannot “see” the entire horizon. This means it might report “Clear” if a cloud is nearby but not directly over the sensor. Industry pros search for “ASOS vs. Satellite cloud cover” to reconcile these differences, especially when verifying “Opacity” or “Sky Cover” forecasts for solar energy providers.
On an ASOS report, “A01” indicates the station does not have a precipitation discriminator (it can’t tell the difference between rain and snow), while “A02” means it does. Forecasters search for “ASOS A02 locations” when they need to verify “Precipitation Type” forecasts, as relying on an A01 station for “Snowfall Actuals” can lead to verification errors.