FAA Aircraft Dispatcher (ADX)MeteorologyEasy
A dispatcher observes on satellite and radar imagery precipitation shafts that appear to descend from cloud bases but evaporate before reaching the ground. This phenomenon is known as:
- AMammatus clouds, indicating a decaying thunderstorm
- BA gust front producing a shelf cloud
- CAn occluded frontal boundary at low levels
- DVirga, which can be associated with strong downdrafts and a potential microburst hazard
Show answer & explanationAnswer & explanation
Correct answer: D. Virga, which can be associated with strong downdrafts and a potential microburst hazard
Virga is precipitation that falls from a cloud but evaporates before reaching the surface, typically occurring when dry air exists below the cloud base. Evaporative cooling associated with virga can accelerate downdrafts and is a known precursor to dry microbursts.
Why the other options are wrong
- A. Mammatus are pouch-like cloud formations, not falling precipitation.
- B. A shelf cloud is a low, wedge-shaped cloud at a thunderstorm's leading edge, not evaporating rain shafts.
- C. An occlusion is a frontal system feature unrelated to visual precipitation shafts.
Virga
Precipitation that falls from a cloud but evaporates in dry air before reaching the ground, sometimes associated with dry microbursts.
- Occurs when air below cloud base is very dry
- Evaporative cooling can accelerate a downdraft
- Associated hazard: dry microbursts, especially in arid regions
Memory trick: Virga vanishes before it lands — but the cold air it drops can slam you