Which METAR code denotes small hail or graupel?

The METAR code that denotes small hail or graupel is represented by the code "GS." In aviation meteorology, GS is specifically used to indicate the presence of small hail or soft hail, also known as graupel, which consists of snow pellets that can fall during certain types of precipitation conditions.

Understanding such codes is essential for pilots and meteorologists, as they provide critical information about weather phenomena that could affect flying conditions. This information aids in assessing the weather's potential impact on flight safety and operations. The other codes listed, while related to weather, refer to different types of precipitation or meteorological phenomena: "GR" denotes larger hail, "PL" refers to ice pellets, and "UP" indicates unknown precipitation. These distinctions are important for correctly interpreting METAR reports.