Definition
In a METAR sky condition group, CLR indicates that no clouds were detected below 12,000 feet AGL by an automated weather observing station. It is reported only by automated stations (ASOS/AWOS) and means the automated sensor found no clouds within its detection range; it does not certify the sky is clear above 12,000 feet.
Plain English
CLR on a METAR means an automated weather station did not detect any clouds below 12,000 feet above the ground. Higher clouds may still exist — the machine simply cannot see them.
Context Anchor
Seen in the sky condition section of a METAR, where cloud cover is reported.
Derivation
CLR is just a shortened form of 'clear.' METARs use compact codes to keep reports short enough to transmit quickly over teletype and radio.
Why Pilots Care
Tells pilots they can expect good visual conditions for VFR flying without low cloud interference.
Intuition Check
Do not read CLR as “there are no clouds anywhere.” In a METAR, CLR means no clouds are reported below 12,000 feet above the ground at that station.
Example Sentence 1
The METAR from the automated field showed CLR, so I knew there were no clouds detected below 12,000 feet, though high cirrus could still be present.
Example Sentence 2
Even with CLR at the departure airport, higher clouds might still affect the route.