AO2
Indicates an automated weather observation station equipped with a precipitation discriminator. AO2 stations can differentiate between liquid and frozen precipitation types, providing more accurate weather reports. Most ASOS (Automated Surface Observing System) stations in the US are AO2 type.
RMK AO2
RMK AO2 SLP135
RMK AO2 RAB25
AO2 stands for "Automated Station Type 2" in the remarks section of a METAR report. Indicates an automated weather observation station equipped with a precipitation discriminator. AO2 stations can differentiate between liquid and frozen precipitation types, providing more accurate weather reports. Most ASOS (Automated Surface Observing System) stations in the US are AO2 type.
AO2 appears in the remarks (RMK) section at the end of a METAR observation. The remarks section follows the main body of the METAR and provides additional details about the observation that don't fit into the standard coded format.
Here is an example: "RMK AO2". This appears in the remarks section and indicates automated station type 2 information as part of the weather observation.