FAA Instrument Flight Instructor (FII)WeatherHard
At a mountain valley airport on a clear, calm night, an ATIS reports gusty surface winds even though winds aloft are light. A CFII explains this is caused by cold, dense air pooling on higher terrain and flowing downhill into the valley under gravity. What is this phenomenon called?
- AAnabatic wind
- BKatabatic (drainage) wind
- CSanta Ana wind
- DChinook wind
Show answer & explanationAnswer & explanation
Correct answer: B. Katabatic (drainage) wind
A katabatic (drainage) wind occurs at night when air near elevated terrain cools and becomes denser than the surrounding air, causing it to flow downslope into valleys under the influence of gravity. This can produce locally gusty surface winds in calm upper-level conditions.
Why the other options are wrong
- A. Anabatic winds flow upslope during the day due to daytime heating, the opposite of this nighttime scenario.
- C. Santa Ana winds are a specific offshore wind pattern in Southern California associated with high pressure inland, not general nighttime drainage.
- D. A Chinook is a warm, dry downslope wind caused by adiabatic compression on the lee side of mountains, not simple gravity drainage of cold air.
Katabatic (Drainage) Wind
A wind caused by cold, dense air flowing downhill from higher terrain into valleys under gravity, typically occurring at night with radiational cooling.
- Opposite of anabatic (upslope, daytime) winds
- Common in mountainous terrain on clear, calm nights
- Can cause locally strong, gusty surface winds despite light winds aloft
Memory trick: Kat-abatic = 'cat creeping downhill'—cold air slinks down at night.