wrote:
/snip/
Does anyone know the practical use of this nugget of AO1/AO2
information? For example, does it mean that an AO1 station reports -RA
for light rain OR light snow? Thanks!

I believe an A01 station will not report the cause of the restriction to
visibility, just the visibility distance. An A02 station will report
what is causing the restriction, such as RA, SN, FG, BR, BLSN, HZ, etc.

Happy Flying!
Scott Skylane