Definition
In a METAR, SA is the contraction used to report sand as a present weather phenomenon — loose grains of sand suspended in or being lifted by the air at or near the surface of the reporting station.
Plain English
SA on a weather report means there is sand in the air at the airport. It is the code weather observers use when sand is blowing around or hanging in the air enough to affect what pilots can see.
Context Anchor
Seen in the weather section of a METAR when the airport is reporting sand in the air.
Derivation
SA is simply a two-letter contraction taken from the first two letters of 'sand.' METAR uses short two-letter codes so weather phenomena can be packed into a compact, standardized report.
Why Pilots Care
Blowing sand sharply cuts visibility and can damage engines or pitot systems.
Grounding Statement
Picture wind picking up loose sand near the airport so the view ahead looks dusty or brownish instead of clear.
Intuition Check
Do not read SA as sand lying on the ground. In a METAR, SA means sand is in the air and affecting the weather report.
Example Sentence 1
The METAR for the desert airfield included SA in the present weather group, so the pilot expected reduced visibility on approach.
Example Sentence 2
Strong winds stirred up SA, dropping visibility to one mile.