FAA Sport Pilot Airplane (SPA)WeatherMedium
During a preflight briefing, a pilot is advised that virga is visible beneath cumulus clouds along the route but that thunderstorms are not yet reported. What hazard should the pilot be most concerned about near these clouds?
- AWidespread advection fog forming beneath the cloud bases
- BFreezing rain at the surface due to warm rain falling through a subfreezing layer
- CA stationary front developing directly beneath the virga
- DA strong, potentially damaging downdraft or microburst caused by evaporative cooling of the falling precipitation
Show answer & explanationAnswer & explanation
Correct answer: D. A strong, potentially damaging downdraft or microburst caused by evaporative cooling of the falling precipitation
Virga is precipitation that evaporates before reaching the ground; the evaporative cooling process can create a strong downdraft, sometimes leading to a dry microburst even in the absence of visible surface rain or a mature thunderstorm.
Why the other options are wrong
- A. Virga is unrelated to fog formation, which requires different moisture/temperature conditions.
- B. Virga does not require a subfreezing surface layer and is not linked to freezing rain.
- C. Virga is a precipitation phenomenon, not a frontal boundary indicator.
Virga
Virga is precipitation that falls from a cloud but evaporates before reaching the surface, often producing a rapid cooling and sinking of air that can generate a dry microburst.
- Visible as streaks trailing beneath cloud base that don't reach ground
- Evaporative cooling accelerates downward air movement
- Associated with dry microburst hazard even without a mature storm
Memory trick: Virga 'vanishes' but leaves a violent gust behind.