FAA Flight Instructor Airplane (FIA)Weather and Weather ServicesEasy
A pilot preparing for an early morning departure from an airport situated in a mountain valley checks the overnight weather log and notices that cold, dense air drained down from the surrounding slopes and pooled near the valley floor, producing gusty surface winds that died out shortly after sunrise. This local wind phenomenon is best classified as a:
- AChinook wind
- BSea breeze
- CGeostrophic wind
- DKatabatic (drainage) wind
Show answer & explanationAnswer & explanation
Correct answer: D. Katabatic (drainage) wind
Katabatic winds occur when cold, dense air at higher elevations flows downhill under the influence of gravity, typically at night when radiational cooling chills air along mountain slopes. They usually dissipate after sunrise as surface heating begins.
Why the other options are wrong
- A. A Chinook is a warm, dry downslope wind caused by adiabatic compression, not cold drainage air.
- B. A sea breeze is caused by differential heating between land and water, not mountain terrain.
- C. Geostrophic wind is an upper-level wind parallel to isobars, unrelated to terrain drainage.
Katabatic Wind
A downslope wind caused by cold, dense air flowing from higher to lower terrain under gravity, most common overnight in mountain valleys.
- Forms from radiational cooling on slopes at night
- Cold air is denser and drains downhill by gravity
- Typically weakens or stops after sunrise heating begins
Memory trick: Katabatic = 'Cat-abatic' cold air creeping down the mountain like a cat sneaking downhill at night