What is the significance of the abbreviation RAB in METAR reports?

The abbreviation RAB in METAR reports signifies that rain has begun. This is important because it helps pilots, meteorologists, and other aviation professionals understand the current weather conditions at an airport. Knowing when rain has started can impact flight operations, including takeoff, landing, and taxiing procedures. It provides crucial information about visibility and runway conditions, which are vital for safe aviation practices.

The other options address different weather phenomena but do not relate directly to the specific meaning of RAB. Rain initiation is significant for operations at airports, making this abbreviation critical in real-time weather reporting and analysis.