Definition
In a METAR or TAF, /RM is a separator code that introduces the Remarks section. Everything after /RM contains supplementary information not included in the main body of the report, such as observed weather phenomena, sea-level pressure, hourly precipitation amounts, and station-specific notes.
Plain English
/RM marks the start of the extra notes at the end of a weather report. Anything written after it is added detail that the main part of the report did not cover.
Context Anchor
Seen in the coded format of PIREPs in aviation weather reports.
Derivation
RM is short for 'Remarks,' from the Latin re- (again) and marcare (to note or mark). A remark is something noted in addition. The slash separates this added section from the standard report body.
Why Pilots Care
Gives pilots a place to report important extra details that can affect safety or route decisions for others.
Intuition Check
Do not read /RM as a runway, radio, or distance code. In a PIREP, /RM simply marks the remarks section.
Example Sentence 1
After decoding the main body of the METAR, the pilot read past /RM and noted that lightning had been observed northwest of the field.
Example Sentence 2
After /RM the pilot added that visibility dropped rapidly near the ridge.