How are "snow grains" expressed in a METAR report?

In a METAR report, "snow grains" are expressed using the code "SG." This term specifically indicates a form of precipitation characterized by small, white, opaque ice particles that fall from the sky. These particles are similar to snowflakes but are usually much smaller and more granular. The use of "SG" allows meteorologists and pilots to quickly understand the type of precipitation occurring at the reporting station.

The other options represent different forms of precipitation or weather phenomena. For example, "SN" is used for standard snow, "SGR" does not represent a recognized weather phenomenon in METARs, and "GR" is typically used to denote hail. Knowing the specific codes helps in the correct interpretation of weather conditions, which is critical for flight safety and operations.