What is the primary observation code to be used in the U.S. for reporting surface meteorological data?

The primary observation code used in the U.S. for reporting surface meteorological data is METAR. This format is widely accepted and utilized for routine reporting of weather conditions at airports and other surface observation stations. METAR reports provide essential information, including temperature, dew point, wind speed and direction, precipitation, and significant weather phenomena, all crucial for aviation and other weather-dependent activities.

METAR is designed to convey clear and concise weather information to pilots, meteorologists, and other stakeholders, making it a reliable and standardized source of data. It follows a specific structure and allows for the timely dissemination of meteorological information, which is critical in maintaining flight safety and operational efficiency.

The other codes listed, such as SA, SAWRS, and synoptic, serve different purposes or have less widespread use in aviation meteorology compared to METAR. For instance, SA refers to surface observations in general when reporting but is not as commonly used as METAR for aviation needs. SAWRS pertains to a specific type of surface observation station, and synoptic can refer to larger-scale meteorological observations, but again, they do not match the specificity and frequency of METAR reporting.