Definition
A remarks-section contraction used in aviation weather reports (such as METARs and pilot reports) to indicate the presence of towering cumulus clouds — tall, rapidly building cumulus clouds with strong vertical development that often signal unstable air and the potential for thunderstorm formation.
Plain English
A short code in a weather report meaning 'towering cumulus' — tall, fast-growing puffy clouds that show the air is unstable and storms may be developing.
Context Anchor
Seen in PIREPs, where each slash code labels a different part of the pilot’s weather report.
Derivation
The slash (/) is a separator commonly used in weather report contractions, and TM is shorthand for Towering Cumulus. The contraction style keeps weather reports compact so they can be transmitted and read quickly.
Why Pilots Care
Tells pilots how recent the reported conditions are so they can judge whether the information still applies to their flight.
Intuition Check
Do not read /TM as a local clock time unless the report says so. In aviation weather reports, the time is normally given in UTC so everyone uses the same reference.
Example Sentence 1
The METAR remarks included /TM to the northwest, so the pilot planned a route that avoided the building cumulus activity.
Example Sentence 2
A later /TM on the same route helped confirm the icing report was only minutes old.