Definition
The rate at which atmospheric temperature decreases with an increase in altitude. The standard (average) lapse rate is approximately 2 °C (3.5 °F) per 1,000 feet of altitude gain.
Plain English
How fast the air gets colder as you climb higher. On average, the temperature drops about 2 °C for every 1,000 feet you gain.
Context Anchor
Seen in weather and atmosphere discussions when comparing surface temperature with temperatures aloft.
Derivation
From 'lapse,' meaning to fall or decline (Latin lapsus, 'a slip or fall'), and 'rate,' meaning how fast something changes. So 'lapse rate' literally means the rate at which something falls — in this case, temperature falling as altitude rises.
Why Pilots Care
Lapse rate affects engine performance, aircraft performance, icing potential, and cloud formation. Knowing the standard rate lets a pilot estimate the temperature at altitude, anticipate icing levels, and judge whether the day's conditions are warmer or colder than standard.
Grounding Statement
If the surface temperature is 15 °C, the temperature at 10,000 feet under standard conditions will be roughly 20 °C colder — about −5 °C.
Intuition Check
Lapse rate is not about time passing or something expiring. In aviation weather, it means how temperature changes with altitude.
Example Sentence 1
Using the standard lapse rate, the pilot estimated the temperature at 8,000 feet would be about 16 °C colder than the surface reading.
Example Sentence 2
A steeper lapse rate can signal unstable air that may produce clouds or turbulence.