Definition
The change in atmospheric pressure at a given station over the past three hours, including both the amount of change (in millibars or hectopascals) and the character of the change (rising, falling, or steady). Reported on surface analysis charts and station models to indicate short-term pressure trends.
Plain English
How much the air pressure at a weather station has gone up or down over the last three hours, and whether it is still climbing, dropping, or holding steady.
Context Anchor
Seen on surface analysis charts and station models, where nearby observations are plotted for pilots and weather briefers.
Derivation
Tendency comes from the Latin tendere, meaning to stretch or move toward. A pressure tendency is the direction the pressure is moving toward — up or down — over a recent stretch of time.
Why Pilots Care
A falling pressure tendency often signals an approaching low or front and possible deteriorating weather.
Grounding Statement
If the pressure at a station has dropped during the last few hours, the pressure tendency is downward even if the current pressure number still looks normal.
Intuition Check
Pressure tendency is not the current pressure reading. It is the recent direction and amount of change in pressure.
Example Sentence 1
The station's pressure tendency showed a steady fall over the past three hours, suggesting a front was moving in.
Example Sentence 2
Pilots review pressure tendency values to anticipate weather changes along their route.