Definition
A method used by automated weather observing systems (such as ASOS/AWSS) in which cloud height and sky cover data are gathered from a single ceilometer over a 30-minute period, and that time-based sample is treated as if it represented conditions across the airport area. Because the sensor only sees the sky directly above it, the system uses time as a substitute for space, assuming clouds drifting overhead during the sampling window approximate the broader sky condition.
Plain English
The automated weather station only looks straight up at one spot, so it watches that spot for half an hour and uses what passes overhead to estimate what the whole sky looks like.
Context Anchor
Seen in ASOS and AWSS discussions, especially when explaining how automated weather stations report visibility and sky conditions from sensor data.
Derivation
Spatial' comes from the Latin spatium, meaning 'space' or 'area.' The technique is called spatial averaging because it produces an estimate covering an area of sky, even though the sensor itself only measures one narrow column. Time-passing-overhead is used as a stand-in for looking around.
Why Pilots Care
Prevents a single sensor near a building or taxiway from producing a misleading wind or visibility value that could affect takeoff, landing, or go/no-go decisions.
Analogy
It is like using one thermostat reading to describe the temperature in a whole room. It may be useful and mostly right, but one corner of the room could still feel different.
Grounding Statement
If fog is thicker at one end of the airport than near the weather sensor, the automated report may describe the general airport condition without showing that local difference.
Intuition Check
Do not assume spatial averaging means the system has checked every part of the airport equally. It means the system uses limited measurements to produce one area-wide estimate.
Example Sentence 1
Because ASOS uses a spatial averaging technique, the reported ceiling reflects only what passed over the ceilometer during the last 30 minutes.
Example Sentence 2
Pilots use reports generated with the spatial averaging technique to judge runway conditions more accurately during approach.