Definition
The horizontal movement of clouds across an area, carried by the prevailing wind. In automated weather observing systems, cloud advection is a recognized limitation because the sensor only detects clouds passing directly overhead, not clouds that may be visible nearby but are being blown across the area without crossing the sensor.
Plain English
Clouds being pushed sideways by the wind from one place to another. An automated weather sensor on the ground can only see clouds that drift directly over it, so clouds moving past off to one side may be missed in the report.
Context Anchor
Seen in automated weather observing discussions, especially where a ground sensor reports clouds as they pass over the airport.
Derivation
Advection comes from the Latin advectio, meaning 'to carry toward.' In meteorology it is used for any horizontal transport by the wind, whether of heat, moisture, or — as here — clouds themselves. Knowing this helps separate advection (sideways movement) from convection (vertical movement).
Why Pilots Care
Rapid changes in reported ceilings and visibility can occur without new cloud development, directly affecting takeoff, landing, and instrument approach decisions.
Grounding Statement
If low clouds are west of the airport and the wind is blowing from west to east, those clouds may soon move over the airport.
Intuition Check
Cloud advection does not mean the cloud is being created over the airport. It means clouds that already exist are being carried across the area by the wind.
Example Sentence 1
Because of cloud advection, the automated station reported clear skies even though a broken layer was visible just north of the field.
Example Sentence 2
Forecasters noted cloud advection from the southwest that lowered ceilings ahead of the arrival.