FAA Private Pilot Airplane (PAR)Weather Theory and ServicesHard
While approaching an area of scattered thunderstorms, a pilot observes streaks of precipitation visible beneath a cloud base that appear to evaporate before reaching the ground. This phenomenon is most significant to the pilot because it can indicate the potential for which hazard?
- AA strong, sudden downdraft or microburst beneath the cloud
- BSteady, predictable precipitation with no turbulence
- CFormation of clear ice on the airframe
- DAn approaching warm front with widespread stratus clouds
Show answer & explanationAnswer & explanation
Correct answer: A. A strong, sudden downdraft or microburst beneath the cloud
Virga is precipitation that evaporates before reaching the surface. The evaporative cooling process can create a dense pocket of cold, heavy air that accelerates downward, potentially producing a strong downdraft or microburst — a serious hazard to aircraft operating below or near the cloud.
Why the other options are wrong
- B. Virga indicates evaporating precipitation, which is associated with hazardous downdrafts, not calm predictable rain.
- C. Clear icing requires supercooled liquid droplets and is not directly related to virga evaporation.
- D. Virga is typically associated with convective clouds, not the stratus clouds of a warm front.
Virga
Virga is precipitation that falls from a cloud but evaporates before reaching the ground; the evaporative cooling can generate a strong downdraft, including microbursts.
- Common beneath cumulonimbus and towering cumulus clouds in dry lower atmosphere
- Evaporative cooling increases air density, accelerating descent
- Can be a visible warning sign of imminent low-level wind shear
Memory trick: 'Vanishing Virga Vents a Vicious downdraft' — evaporating rain can trigger a violent sinking wind.